ARM64: dts: meson-gxbb: Add P20x Wifi SDIO support

Add Wifi module support on the Amlogic P20x boards on the SDIO port.
The Wifi module also needs a 32768Hz clock provided by the PWM E port
through a pwm-clock node in it's power sequence.

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