drm/amdgpu: add basic func for RLC program reg

New feature for RLC, some registers can be programmed by
RLC interface under SR-IOV VF:

WREG32_SOC15_RLC_SHADOW:
	1, for GRBM_GFX_CNTL, firstly the new register value should be be
		programmed to SCRATCH_REG2
	1, for GRBM_GFX_INDEX, firstly the new register value should be be
		programmed to SCRATCH_REG3

WREG32_RLC:
	for registers supported to be programmed by RLC interface, the
	following sequence should be used:
		1, write the value to SCRATCH_REG0
		2, write reg | 0x80000000 to SCRATCH_REG1
		3, write 0x1 to RLC_SPARE_INT to notify RLC
		4, polling SCRATCH_REG1 to check if finished

Signed-off-by: Trigger Huang <Trigger.Huang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>