drm/amdkfd: Enable GWS based on FW Support

Rather than only enabling GWS support based on the hws_gws_support
modparm, also check whether the GPU's HWS firmware supports GWS.
Leave the old modparm in place in case users want to test GWS
on GPUs not yet in the support list.

v2: fix broken syntax from the first patch.

Signed-off-by: Joseph Greathouse <Joseph.Greathouse@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>