ramips: mt7620: add missing PA/LNA pinctrl for Linksys E1700

ramips: mt7620: add missing PA/LNA pinctrl for Linksys E1700

This device has high-power external PA and LNA[1]. So we must
configure PA/LNA pins to make the wireless work properly.

[1] https://fccid.io/Q87-E1700/Internal-Photos/Internal-Photos-pdf-2135639.pdf
Fixes: https://github.com/openwrt/openwrt/issues/7959
Signed-off-by: Shiji Yang <yangshiji66@qq.com>
Link: https://github.com/openwrt/openwrt/pull/17892
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
(cherry picked from commit 3aa9b708364fd4a46c8466750f51069e22f3dde7)