drm/amd/display: Add chip mask to HDMI retimer/redriver check

There were cases where the chip caps held additional bits that led to
the retimer/redriver check failing; use the proper mask to ensure that
we have only the bits that we care about for the check in question.

Signed-off-by: Andrew Jiang <Andrew.Jiang@amd.com>
Reviewed-by: Charlene Liu <Charlene.Liu@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>