arm64: dts: meson-g12-common: add spicc controller nodes

This adds the controller and pinctrl nodes for the Amlogic G12A SPICC
controllers.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Link: https://lore.kernel.org/r/20200313091401.15888-1-narmstrong@baylibre.com