drm/amd/display: Update TX masks correctly

[Why]
Bugs occur when TX interrupt comes in when no USB-C on board.

[How]
Check PHY for USB-C before enabling TX interrupt in DMCU FW.

Signed-off-by: Alvin Lee <alvin.lee2@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>