[atheros] [mips] Add the GPIO driver (back) to the TL-WDR3600/TL-WDR4300 kernel.

So it turns out that sometime in the past I removed the GPIO bits here
and was going to move it into a module in order to save a little space.
However, it turns out that was a mistake on this particular AP - it
uses a pair of GPIO lines to control the two receive LNAs on the 2GHz
radio and without them enabled the radio is a LOT DEAF.

With this re-introduced (and some replacement userland tools to save
space, *cough* cpio/libarchive) I can actually use these chipsets
again as a 2G station.  Without the LNA the AP was seeing a per-radio
RSSI upstairs here of around 3-5dB, with the LNA on it's around 15dB,
more than enough to actually use wifi upstairs and also in line with
the other Atheros / Intel devices I have up here.

Big oopsie to Adrian.  Big, big oopsie.

sys/mips/conf/TL-WDR4300

@@ -50,5 +50,12 @@ options 	AR71XX_ATH_EEPROM
 device		firmware		# Used by the above
 options 	ATH_EEPROM_FIRMWARE
 
+options 	ATH_DEBUG_ALQ
+
 # Boot off of the rootfs, as defined in the geom_map setup.
 options 	ROOTDEVNAME=\"ufs:map/rootfs.uzip\"
+
+# This is required for the 2GHz LNAs on the AR9340 SoC.
+# Without this the 2GHz radio is Quite Deaf.
+device		gpio
+device		gpioled