pcm support for AR9341

From: Mori Hiroki <yamori813_at_yahoo.co.jp>
Date: Sat, 19 Feb 2022 04:03:36 UTC 
Hi

I add pcm support for AR9341.

https://github.com/ZRouter/freebsd-src/tree/yamori813_modify

AR9341 have gpio pin multiplexing. This is very useful. 

I add SPDIF TOSLINK on not use GPIO12. And set hints.

# SPDIF_OUT
hint.gpio.0.func.12.gpiofunc=25
hint.gpio.0.func.12.gpiomode=1

Thanks

Hiroki Mori