drm/meson: add AFBC decoder registers for GXM and G12A

Add the registers used to program the ARM Framebuffer Compression decoders
used in the Amlogic GXM and G12A SoCs families.

This also adds the routing and pipeline configuration bits and registers
needed to enable AFBC support.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Kevin Hilman <khilman@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191021091509.3864-2-narmstrong@baylibre.com