ramips: reset mt7620 ethernet phy via reset controller

ramips: reset mt7620 ethernet phy via reset controller

Use reset controller to reset mt7620 ethernet phy instead of directly
writing system control registers. The reset line of "ephy" is 24, so
the DTS resets properties have been updated to get the correct reset
signal.

Tested on HiWiFi HC5861.

Signed-off-by: Shiji Yang <yangshiji66@qq.com>