drm/amd/display: Set new format info for converted metadata.

If we use DCC modifiers this can increase the number of planes from
the initial 1 plane with metadata, so that we get a valid modifier
from getfb2.

Since the code didn't update the format_info getfb2 would only ever
return 1 plane with a modifier for which userspace expects > 1.

This moves the format lookup to amdgpu_display.c so we do not have
issues when DC is not compiled.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>