drm/amd/amdkfd: Surface files in Sysfs to allow users to get number of

compute units that are in use.

[Why]
Allow user to know how many compute units (CU) are in use at any given
moment.

[How]
Surface files in Sysfs that allow user to determine the number of compute
units that are in use for a given process. One Sysfs file is used per
device.

Signed-off-by: Ramesh Errabolu <Ramesh.Errabolu@amd.com>
Reviewed-By: Harish Kasiviswanathan <Harish.Kasiviswanathan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>