This code was written prior to previous updates to this
logic for other chips.  The RSC registers are part of
SMUIO which is an always on block so there is no need
to disable gfxoff.  Additionally add the carryover and
preemption checks.

v2: rebase
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>