ramips-mt7620: add support for Netgear EX3700/EX3800

Specifications:
* SoC: MT7620A
* RAM: 64 MB DDR
* Flash: 8MB NOR SPI flash
* WiFi: MT7612E (5Ghz) and builtin MT7620A (2.4GHz)
* LAN: 1x100M

The -factory images can be flashed from the device's web
interface or via nmrpflash.

Both devices differ by a additional power outlet for the EX3800.
This patch has been tested on a EX3800 device.

package/gluon-core/luasrc/lib/gluon/upgrade/010-primary-mac

@@ -111,6 +111,7 @@ local primary_addrs = {
 			'c20i',
 			'c50',
 			'tplink,c2-v1',
+			'ex3700'
 		}},
 		{'x86'},
 	}},

targets/ramips-mt7620

@@ -20,6 +20,15 @@ device('gl-mt750', 'gl-mt750', {
 	factory = false,
 })
 
+-- Netgear
+
+device('netgear-ex3700', 'ex3700-ex3800', {
+	aliases = {
+		'netgear-ex3800',
+		'netgear-ex3700-ex3800',
+	},
+	factory_ext = '.chk',
+})
 
 -- Nexx