[][pwm add mt7981 support]

[Description]
Add PWM dts node, remove PWM clock from clkitg, modify PWM drivers for REG-V2.

[Release-log]
N/A

Change-Id: If007b311f77d9a2fa4be26199b63ff384d0218c0
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/5381846
3 files changed