drm/amd/display: Only require EDID read for HDMI and DVI

[Why]
VGA sometimes has trouble retrieving the EDID on very long cables, KVM
switches, or old displays.

[How]
Only require EDID read for HDMI and DVI and exempt other types (DP,
VGA). We currently don't support VGA but if anyone adds support in the
future this might get overlooked.

Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Suggested-by: Michel Dänzer <michel@daenzer.net>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>