drm/amd/display: Workaround for some legacy DP-VGA dongles

[Why]
Maximum resolution is 1440*900 when connecting to FHD monitor via some DP-VGA
dongles. The display EDID reading fails over AUX/I2C via DP->VGA dongle, and
this leads to the maximum resolution 1920*1080 cannot be obtained from EDID.

[How]
Provide a workaround for some legacy DP-VGA dongles with a longer aux delay.

Signed-off-by: Taimur Hassan <syed.hassan@amd.com>
Reviewed-by: Wenjing Liu <Wenjing.Liu@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>