[][Add mt79xx audio platform and machine driver]

[Description]
Add mt79xx audio platform and machine driver with wm8960 and si3218x

Patch reference: https://lore.kernel.org/alsa-devel/1573814926-15805-2-git-send-email-eason.yen@mediatek.com/T/

[Release-log]
N/A

Change-Id: I316c562e20d118899a38206cc1fd4c6e14bffdbd
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/5397355
18 files changed