Add implementation to program regs by PSP, currently the following
IH registers are supported:
	IH_RB_CNTL
	IH_RB_CNTL_RING1
	IH_RB_CNTL_RING2
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>