ramips: mt7621: add missing regulator-boot-on

ramips: mt7621: add missing regulator-boot-on

What seems to be happening is that the kernel requests an ACTIVE_LOW
gpio initially and sets it to high later based on gpios in dts.

This seems to break some devices where the bootloader sets it to high.

Fixes: e612900ae0 ("ramips: mt7621: convert usb power to regulators")
Signed-off-by: Rosen Penev <rosenp@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/16877
Signed-off-by: Robert Marko <robimarko@gmail.com>