drm/meson: viu: add AFBC modules routing functions

The Amlogic G12A AFBC Decoder pixel input need to be routed diferently
than the Amlogic GXM AFBC decoder, this adds support for routing the
VIU OSD1 pixel source to the AFBC "Mali Unpack" module.

This "Mali Unpack" module is also configured with a static RGBA mapping
for now until we support more pixel formats.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Kevin Hilman <khilman@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191021091509.3864-8-narmstrong@baylibre.com