drm/aspeed: Allow both DVO and VGA outputs modes.
Allow both output-vga and output-dvo to be set in the device tree. Previously, if both were set, only DVO would be enabled in crtl2. This also ensures that output_mode is properly initialized. Previously, output_mode was ORed uninitialized, which could have resulted in both DVO and VGA mode being enabled unexpectedly.
Signed-off-by: Evan Lojewski github@meklort.com