drm/amd/display: Fix TMDS 4K@60Hz YCbCr420 corruption issue

[Why]
DIG_FIFO_OUTPUT_PIXEL_MODE not being set for dcn314
resulting in incorrect timing for YCbCr4:2:0

[How]
Copy the implementation of set_pixels_per_cycle from dcn32
over to dcn314

Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: Tom Chung <chiahsuan.chung@amd.com>
Signed-off-by: Daniel Miess <Daniel.Miess@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>