arm64: dts: mt7986: add PWM to BPI-R3

Add pwm node and pinctrl to BananaPi R3 devicetree.

Signed-off-by: Frank Wunderlich <frank-w@public-files.de>
Link: https://lore.kernel.org/r/20230421132047.42166-6-linux@fw-web.de


Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>