ramips: Add support for Xiaomi MiWiFi Nano

Xiaomi MiWiFi Nano is based on Mediatek MT7628 with 64MB ram 16MB flash

Signed-off-by: Noble Pepper <openwrtmail@noblepepper.com>

v3  includes changes suggested by L. D. Pinney & Karl Palsson-
Eliminate en25q64 (4MB) flash chip
Alphabetization
Remove hyphen in model
Rename profile from miwifinano.mk to xiaomi.mk
Add gpios that are attached to leds

SVN-Revision: 49024