drm/amd/display: Always write repeater mode regardless of LTTPR

[WHY]
SCR for DP2.0 requires that LT be performed with PHY_REPEATER_MODE
programmed to 0x55 (Transparent) whenever PHY_REPEATER_CNT is any value
other than 0x80, 0x40, 0x20, 0x10, 0x08, 0x04, 0x02, or 0x01.

[HOW]
Write Non-Transparent (0xAA) to PHY_REPEATER_MODE when LTTPRs detected and Non-Transparent is
requested.
Write Transparent in all other cases.

Signed-off-by: Wesley Chalmers <Wesley.Chalmers@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Anson Jacob <Anson.Jacob@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>