dt-bindings: serial: amlogic,meson-uart: Add compatible string for G12A

dt-bindings: serial: amlogic,meson-uart: Add compatible string for G12A

Amlogic G12A SoCs gained a new "divide XTAL by 2" bit. Everything else
(we know about) is identical to the UART IP on GX (GXBB/GXL/GXM) SoCs.
Add a new compatible string for this SoC so this new bit can be managed
accordingly while keeping "amlogic,meson-gx-uart" as fallback compatible
string.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230307222651.2106615-2-martin.blumenstingl@googlemail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>