ARM: dts: Add missing DT for Meson G12A support

The following DT nodes in the process on review for Linux 5.3,
until Linux 5.3 is tagged, add the missing DT nodes in u-boot specific
DTSI files that will be dropped when the v5.3-rc1 DT is synced again.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>