drm/amdkfd: show warning when kfd is locked

During system suspend the kfd driver aquires a lock that prohibits
further kfd actions unless the gpu is resumed. This adds some info which
can be useful while debugging.

Reviewed-by: Oak Zeng <oak.zeng@amd.com>
Reviewed-by: Felix Kuehling <felix.kuehling@amd.com>
Signed-off-by: Rajneesh Bhardwaj <rajneesh.bhardwaj@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>