ocf: do not build ocf_inc and ocf_src concurrently

Those targets use the same directories for temporary
files and at the moment they race with each other. We're
seeing intermittent failures on CI:

```
INSTALL [...]/ocf/env/src/ocf/utils/utils_list.c
rm: missing operand
```

```
INSTALL [...]/ocf/env/src/ocf/utils/utils_device.h
INSTALL [...]/ocf/env/src/ocf/utils/utils_io.c
rm: cannot remove [...]/ocf/env/src/ocf/utils': Directory not empty
```

Fixes #709

Change-Id: I9bf6ee7a97144afafbb643a0e350f38abe79270f
Signed-off-by: Darek Stojaczyk <dariusz.stojaczyk@intel.com>
Reviewed-on: https://review.gerrithub.io/c/spdk/spdk/+/447750


Reviewed-by: Vitaliy Mysak <vitaliy.mysak@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>
Reviewed-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>