ath79: add Cisco Meraki Z1

ath79: add Cisco Meraki Z1

Specifications:

SOC:	Atheros AR9344 @ 560MHz
RAM:	2x Winbond W9751G6KB-25 (128 MiB)
FLASH:	Hynix H27U1G8F2BTR (128 MiB)
WIFI1:	Atheros AR9340 5.0GHz (SoC)
WIFI2:	Atheros AR9280 2.4GHz
SWITCH:	Atheros AR8236 (5x Gigabit (1x WAN, 4x LAN)
LED:	1x Power-LED, 1 x RGB Tricolor-LED
INPUT:	One Reset Button
USB:	One USB 2.0 Port
UART:	JP1 on PCB (Labeled UART), 3.3v-Level, 115200n8
        (GND, TX, RX, VCC - GND is next to the UART silk screen)

Flashing Instructions:

Since this device is brought over from an old AR71xx, there's
already a wiki-page with detailed instructions:
<https://openwrt.org/toh/meraki/z1>

The gist:
1. Get a root-shell on the device (see wiki). (needs UART access)
2. make a backup (to a PC/safe location) of the existing Meraki
   firmware.
3. copy over the OpenWrt initramfs kernel for the Z1.
   This gets written into the kernel NAND partition.
   (Verify that written image is complete!)

After the following reboot and successfull boot of the staging
OpenWrt initramfs image:

4. copy over the sysupgrade.bin for the router and use sysupgrade
   to make the installation permanent.

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