drm/meson: Add G12A Support for VPP setup

Amlogic G12A needs a different VPP setup code, handle it here.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Tested-by: Jerome Brunet <jbrunet@baylibre.com>
Reviewed-by: Jerome Brunet <jbrunet@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190325141824.21259-4-narmstrong@baylibre.com