drm/amd/display: Hook up CRC capture support for dce120

[Why]
Many IGT tests require CRC capture in order to confirm that the output
is visually correct.

These skip on dce120 because configure_crc and get_crc aren't set.

[How]
Hook up is_tg_enabled, configure_crc and get_crc functions on dce120's
timing generator.

The logic should be the same as DCE and DCN with some minor register
naming differences.

Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: David Francis <David.Francis@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>