drm/meson: Add registers for G12A SoC

This patch adds the new VPU registers added since the
Amlogic GXM SoCs.

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/20190325141824.21259-3-narmstrong@baylibre.com