ath79: Fix led nodes for TL-WR740N v2 and add its clones

ath79: Fix led nodes for TL-WR740N v2 and add its clones

This patch did the following things:
1. Separate ath9k-leds out of gpio leds so that all other leds will work
   before ath9k loded (e.g. during preinit/init stage).
2. Rename wps led to qss since that's how TP-Link mark it.
3. Rename LED prefix to tp-link because that dts is shared by many devices.
4. Rename to wr740n-v1 because v1 is the first and v2 just use the fw of v1.
   (This will require a forced sysupgrade if you comes from
   the previous wr740n v2 image.)
5. Remove SUPPORTED_DEVICES.
   (tl-wr740n-v2 doesn't exist anywhere so it's useless.)
6. Add all WR741ND v1 clones found in ar71xx.

Signed-off-by: Chuanhong Guo <gch981213@gmail.com>