ath79: define switch reset-gpios for D-Link DIR-842

GPIO 11 needs to be pulled high for the external gigabit switch to work,
this is currently solved via gpio-hog. Replace with phy0 reset-gpios.

Tested on revisions C1 and C3. Reset button is still working for reboot,
to enter failsafe, and to enter bootloader http recovery.

Signed-off-by: Sebastian Schaper <openwrt@sebastianschaper.net>