ipq40xx: add support for ASUS RT-AC58U/RT-ACRH13

ipq40xx: add support for ASUS RT-AC58U/RT-ACRH13

This patch adds support for ASUS RT-AC58U/RT-ACRH13.

hardware highlights:

SOC:	IPQ4018 / QCA Dakota
CPU:	Quad-Core ARMv7 Processor rev 5 (v7l) Cortex-A7
DRAM:	128 MiB DDR3L-1066 @ 537 MHz (1074?) NT5CC64M16GP-DI
NOR:	2 MiB Macronix MX25L1606E (for boot, QSEE)
NAND:   128 MiB Winbond W25NO1GVZE1G (cal + kernel + root, UBI)
ETH:    Qualcomm Atheros QCA8075 Gigabit Switch (4 x LAN, 1 x WAN)
USB:    1 x 3.0 (via Synopsys DesignWare DWC3 controller in the SoC)
WLAN1:  Qualcomm Atheros QCA4018 2.4GHz 802.11bgn 2:2x2
WLAN2:  Qualcomm Atheros QCA4018 5GHz 802.11a/n/ac 2:2x2
INPUT:	one Reset and one WPS button
LEDS:	Status, WAN, WIFI1/2, USB and LAN (one blue LED for each)
Serial:
	WARNING: The serial port needs a TTL/RS-232 3V3 level converter!
	The Serial setting is 115200-8-N-1. The board has an unpopulated
	1x4 0.1" header. The pinout (VDD, RX, GND, TX) is printed on the
	PCB right next to the connector.

U-Boot Note: The ethernet driver isn't always reliable and can sometime
time out... Don't worry, just retry.

Access via the serial console is required. As well as a working
TFTP-server setup and the initramfs image. (If not provided, it
has to be built from the OpenWrt source. Make sure to enable
LZMA as the compression for the INITRAMFS!)

To install the image permanently, you have to do the following
steps in the listed order.

1. Open up the router.
   There are four phillips screws hiding behind the four plastic
   feets on the underside.

2. Connect the serial cable (See notes above)

3. Connect your router via one of the four LAN-ports (yellow)
   to a PC which can set the IP-Address and ssh and scp from.

   If possible set your PC's IPv4 Address to 192.168.1.70
   (As this is the IP-Address the Router's bootloader expects
   for the tftp server)

4. power up the router and enter the u-boot
   choose option 1 to upload the initramfs image. And follow
   through the ipv4 setup.

Wait for your router's status LED to stop blinking rapidly and
glow just blue. (The LAN LED should also be glowing blue).

3. Connect to the OpenWrt running in RAM

   The default IPv4-Address of your router will be 192.168.1.1.

   1. Copy over the openwrt-sysupgrade.bin image to your router's
      temporary directory

   # scp openwrt-sysupgrade.bin root@192.168.1.1:/tmp

   2. ssh from your PC into your router as root.

   # ssh root@192.168.1.1

   The default OpenWrt-Image won't ask for a password. Simply hit the Enter-Key.

   Once connected...: run the following commands on your temporary installation

   3. delete the "jffs2" ubi partition to make room for your new root partition

   # ubirmvol /dev/ubi0 --name=jffs2

   4. install OpenWrt on the NAND Flash.

   # sysupgrade -v /tmp/openwrt-sysupgrade.bin

   - This will will automatically reboot the router -

Signed-off-by: Christian Lamparter <chunkeey@gmail.com>