drm/edid: Move validate_displayid() drm_find_displayid_extension()

Instead of everyone having to call validate_displayid() let's just
have drm_find_displayid_extension() do it for them.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200313162054.16009-6-ville.syrjala@linux.intel.com


Reviewed-by: Alex Deucher <alexander.deucher@amd.com>