drm/amd/display: Support CW4 for DMUB ringbuffer inbox

[Why]
Region 4 is non cacheable and slower than using cache window 4.

[How]
Check the firmware version to determine how we should program the
base address and memory windows.

Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>