ath79: add support for Alcatel HH40V

ath79: add support for Alcatel HH40V

The Alcatel HH40V is a CAT4 LTE router used by various ISPs.

Specifications
==============

SoC: QCA9531 650MHz
RAM: 128MiB
Flash: 32MiB SPI NOR
LAN: 1x 10/100MBit
WAN: 1x 10/100MBit
LTE: MDM9607 USB 2.0 (rndis configuration)
WiFi: 802.11n (SoC integrated)

MAC address assignment
======================

There are three MAC addresses stored in the flash ROM, the assignment
follows stock. The MAC on the label is the WiFi MAC address.

Installation (TFTP)
===================

1. Connect serial console
2. Configure static IP to 192.168.1.112
3. Put OpenWrt factory.bin file as firmware-system.bin
4. Press Power + WPS and plug in power
5. Keep buttons pressed until TFTP requests are visible
6. Wait for the system to finish flashing and wait for reboot
7. Bootup will fail as the kernel offset is wrong
8. Run "setenv bootcmd bootm 0x9f150000"
9. Reset board and enjoy OpenWrt

Installation (without UART)
===========================

Installation without UART is a bit tricky and requires several steps too
long for the commit message. Basic steps:

1. Create configure backup
2. Patch backup file to enable SSH
3. Login via SSH and configure the new bootcmd
3. Flash OpenWrt factory.bin image manually (sysupgrade doesn't work)

More detailed instructions will be provided on the Wiki page.

Tested by: Christian Heuff <christian@heuff.at>
Signed-off-by: Andreas Böhler <dev@aboehler.at>