ARM: dts: meson8: add the PWM_E and PWM_F pins

This adds the definition of the PWM_E (CBUS) and PWM_F (AOBUS) to
meson8.dtsi, allowing devices to use them. PWM_E can be used on some
devices to generate the 32.768kHz clock for the SDIO wifi module, while
PWM_F can be used to control the power LED.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>