drm/amdgpu: add a new set of rlc function pointers

Different asics tend to have different ways to interact
with the RLC.  This just covers enter/exit of safe mode
for updating CG and PG state, but could be extended to
cover other RLC operations in the future if necessary.

Acked-by: Tom St Denis <tom.stdenis@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>