ipq40xx: add support for Buffalo WTR-M2133HP

ipq40xx: add support for Buffalo WTR-M2133HP

Buffalo WTR-M2133HP is a Tri-Band router based on IPQ4019.

Specification
-------------
- SoC: Qualcomm IPQ4019
- RAM: 512MiB
- Flash Memory: NAND 128MiB (MXIC MX30LF1G18AC)
- Wi-Fi: Qualcomm IPQ4019 (2.4GHz, 1ch - 13ch)
- Wi-Fi: Qualcomm IPQ4019 (5GHz, 36ch - 64ch)
- Wi-Fi: Qualcomm QCA9984 (2T2R, 5GHz, 100ch - 140ch)
- Ethernet: 4x 10/100/1000 Mbps (1x WAN, 3x LAN)
- LED: 4x white LED, 4x orange LED, 1x blue LED
- USB: 1x USB 3.0 port
- Input: 2x tactile switch, 2x slide switch (2x SP3T)
- Serial console: 115200bps, pinheader JP5 on PCB
- Power: DC 12V 2A

Flash instruction
-----------------
1. Set up a TFTP server (IP address: 192.168.11.10)
2. Rename "initramfs-fit-uImage.itb" to "WTR-M2133HP-initramfs.uImage"
   and put it into the TFTP server directory.
3. Connect the TFTP server and WTR-M2133HP.
4. Hold down the AOSS button, then power on the router.
5. After booting OpenWrt initramfs image, connect to the router by SSH.
6. Transfer "squashfs-nand-factory.ubi" to the router.
7. Execute the following commands.
    # ubidetach -p /dev/mtd15
    # ubiformat /dev/mtd15 -f /tmp/openwrt-ipq40xx-generic-buffalo_wtr-m2133hp-squashfs-nand-factory.ubi
    # fw_setenv bootcmd bootipq
8. Perform reboot.

Recover to stock firmware
-------------------------
1. Execute the following command.
    # fw_setenv bootcmd bootbf
2. Reboot and wait several minutes.

Signed-off-by: Yanase Yuki <dev@zpc.sakura.ne.jp>