drm/amdgpu: refine gprs init shaders to check coverage

Add codes to check whether all SIMDs are covered, make sure that all
GPRs are initialized.

Signed-off-by: Dennis Li <Dennis.Li@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>