drm/amdgpu: add kgd hw debug mode setting interface

Introduce the require KGD debug calls that will execute hardware debug
mode setting.

Signed-off-by: Jonathan Kim <jonathan.kim@amd.com>
Reviewed-by: Felix Kuehling <felix.kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>