drm/meson: crtc: handle commit of Amlogic FBC frames

Since the VD1 Amlogic FBC decoder is now configured by the overlay driver,
commit the right registers to decode the Amlogic FBC frame.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Tested-by: Kevin Hilman <khilman@baylibre.com>
Reviewed-by: Kevin Hilman <khilman@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200703080728.25207-7-narmstrong@baylibre.com