drm/amd/display: Program DIG FE source select for DVI before PHY en

[Description]
In newer DCN's the programming of SYMCLK_FE_SRC_SEL depends on
the value of DIG_FE_SOURCE_SELECT. If DIG_FE_SOURCE_SELECT is not
already programmed at the time of PHY / DIG enable then the FW
sequence will program an incorrect SYMCLK source. Ensure that we
program DIG_FE_SOURCE_SELECT for all DIO scenarios (DVI in this
particular case) before going through the PHY / DIG enable sequence.

Reviewed-by: Wenjing Liu <wenjing.liu@amd.com>
Acked-by: Zaeem Mohamed <zaeem.mohamed@amd.com>
Signed-off-by: Alvin Lee <alvin.lee2@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>