docs: update accel framework docs

acceleration capabilities. ISA/L is used for optimized CRC32C calculation within

the software module.

The framework includes an API for getting the current capabilities of the

selected module. See [`spdk_accel_get_capabilities`](https://spdk.io/doc/accel__engine_8h.html) for more details.

For the software module, all capabilities will be reported as supported. For the hardware modules, only functions

accelerated by hardware will be reported however any function can still be called, it will just be backed by

software if it is not reported as a supported capability.

## Acceleration Framework Functions {#accel_functions}

Functions implemented via the framework can be found in the DoxyGen documentation of the

standard SPDK model for callbacks with a callback argument.

If the acceleration framework is started without initializing a hardware module,

optimized software implementations of the functions will back the public API.

Additionally, if any hardware module does not support a specific function and that

hardware module is initialized, the specific function will fallback to a software

optimized implementation.  For example, IOAT does not support the dualcast function

in hardware but if the IOAT module has been initialized and the public dualcast API

is called, it will actually be done via software behind the scenes.

optimized software implementations of the operations will back the public API. All

operations supported by the framework have a backing software implementation in

the event that no hardware accelerators have been enabled for that operation.

When multiple hardware engines are enabled the framework will assign each operation to

an engine based on the order in which it was initialized. So, for example if two modules are

enabled, IOAT and software, the software engine will be used for every operation except those

supported by IOAT.

## Acceleration Low Level Libraries {#accel_libs}

way needs to be certain that the underlying hardware exists everywhere that it runs.

The low level library for IOAT is located in `/lib/ioat`.  The low level library

for DSA is in `/lib/idxd` (IDXD stands for Intel(R) Data Acceleration Driver).

In `/lib/idxd` folder, SPDK supports to leverage both user space and kernel space driver

to drive DSA devices. And the following describes each usage scenario:

for DSA and IAA is in `/lib/idxd` (IDXD stands for Intel(R) Data Acceleration Driver and

supports both DSA and IAA hardware accelerators). In `/lib/idxd` folder, SPDK supports the ability

to use either user space and kernel space drivers. The following describes each usage scenario:

Leveraging user space idxd driver: The DSA devices are managed by the user space

Leveraging user space idxd driver: The DSA devices are managed by the SPDK user space

driver in a dedicated SPDK process, then the device cannot be shared by another

process. The benefit of this usage is no kernel dependency.

Leveraging kernel space driver: The DSA devices are managed by kernel

space drivers. And the Work queues inside the DSA device can be shared among

different processes. Naturally, it can be used in cloud native scenario. The drawback of

this usage is the kernel dependency, i.e., idxd driver must be supported and loaded

this usage is the kernel dependency, i.e., idxd kernel driver must be supported and loaded

in the kernel.

## Acceleration Plug-In Modules {#accel_modules}

users can use the `accel-config` command to configure the work queues(WQs) of

the idxd devices managed by the kernel with the following steps:

Note: this library must be installed before you run `configure`

```bash

accel-config disable-wq dsa0/wq0.1

accel-config disable-device dsa0