nvme: move the features definition before the spdk_nvme_cmd

We will add the cdw11 specific commands definition in the next patch,
all the features definition will be reused, so just move the code
to the right place, no code was added with this patch.

Change-Id: I6186523cf1875ab0576f19957ae4c31733e4a8a6
Signed-off-by: Changpeng Liu <changpeng.liu@intel.com>
Reviewed-on: https://review.gerrithub.io/c/spdk/spdk/+/476839


Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Shuhei Matsumoto <shuhei.matsumoto.xt@hitachi.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>