[][dts: mt7986: Fix & isolate pinctrl & flash partition]

[Description]
Fix and isolate pinctrl & flash partition:
1. There are common parts for pinctrl, which we used to
put them in dts. Isolate them into dtsi to avoid lots of
repetition.
2. Isolate flash fixed-partitions so we could modify
easily.

[Release-log]
N/A

Change-Id: Ie4c8add82924445bd00b9139ff4f1a0177eb55ec
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/5053659
5 files changed