[][openwrt][mt7988][audio][Add si3218x-spi and si3218x driver to Kconfig and Makefile]

[Description]
Add si3218x-spi and si3218x driver to Kconfig and Makefile.
Comment out si3218x b/c one must sign NDA with Silicon Labs
to obtain si3218x slic driver.

For Silicon Labs slic driver further information:
Contact window: EDOM TECHNOLOGY CO., LTD
Tel: 02-2657-8811
Web: www.edom.com.tw

[Release-log]
N/A

Change-Id: I727412a0ce731a3c3906aac2f934c66dbbaed21c
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/8249672
1 file changed