ARM: dts: meson8: add the SDXC_A pins

Add the pins for the SDHC MMC controller which connect to the SDIO wifi
on some boards.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20230321171213.2808460-3-martin.blumenstingl@googlemail.com


Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>