drm/amd/display: Allow dmu_stg to support cached inbox for dmub

[Why]
FW version check doesn't allow dmu_stg to support cached inbox,
which yields much better performance than region 4.

[How]
Check a range of fw versions, rather than a simple greater than check.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Wyatt Wood <wyatt.wood@amd.com>
Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: Anson Jacob <anson.jacob@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>