ramips: add support for Netgear JWNR2010 v5

ramips: add support for Netgear JWNR2010 v5

Specification:
 - CPU: MediaTek MT7620N (580 MHz)
 - Flash size: 4 MB NOR SPI
 - RAM size: 32 MB DDR1
 - Bootloader: U-Boot
 - Wireless: MT7620N 2x2 MIMO 802.11b/g/n (2.4 GHz)
 - Switch: MT7620 built-in 10/100 switch with vlan support
 - Ports: 4x LAN, 1x WAN
 - Others: 7x LED, Reset button, UART header on PCB (57600 8N1)

Flash instructions:
 1. Use ethernet cable to connect router with PC/Laptop, any router
    LAN port will work.
 2. To flash openwrt we are using nmrpflash[1].
 3. Flash commands:
      First we need to identify the correct Ethernet id.

        nmrpflash -L

        nmrpflash -i net* -f openwrt-ramips-mt7620-netgear_jwnr2010-v5-squashfs-factory.img

      This will show something like "Advertising NMRP server on net*..." (net*, *=1,2,3... etc.)

 4. Now remove the power cable from router back side and immediately connect it again.
    You will see flash notification in CMD window, once it says reboot the device just
    plug off the router and plug in again.

Revert to stock:
 1. Download the stock firmware from official netgear support[2].
 2. Follow the same nmrpflash procedure like above, this time just use the stock firmware.

        nmrpflash -i net* -f N300-V1.1.0.54_1.0.1.img

MAC addresses on stock firmware:
LAN = *:28 (label)
WAN = *:29
WLAN = *:28

On flash, the only valid MAC address is found in factory 0x4.

Special Note:
 This openwrt firmware will also support other netgear N300 routers like below as they
 share same stock firmware[3].
 JNR1010v2 / WNR614 / WNR618 / JWNR2000v5 / WNR2020 / WNR1000v4 / WNR2020v2 / WNR2050

[1] https://github.com/jclehner/nmrpflash
[2] https://www.netgear.com/support/product/JWNR2010v5.aspx
[3] http://kb.netgear.com/000059663

Signed-off-by: Shibajee Roy <ador250@protonmail.com>
[create DTSI, use netgear_sercomm_nor, disable by default, add MAC
addresses to commit message, add label MAC address]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>