ath79: add support for D-Link DIR-859 A1

ath79: add support for D-Link DIR-859 A1

Hardware spec of DIR-859 A1:
SoC: QCA9563
DRAM: 64MB DDR2
Flash: 16MB SPI-NOR
Switch: QCA8337N
WiFi 5.8GHz: QCA9880

USB is supported on the PCB but not connected.

Flash instructions:

1. Upgrade the factory.bin through the factory web interface or the u-boot
   failsafe interface.
   The firmware will boot up correctly for the first time.
   Do not power off the device after OpenWrt has booted. Otherwise the u-boot
   will enter failsafe mode as the checksum of the firmware has been changed.
2. Upgrade the sysupgrade.bin in OpenWrt.
   After upgrading completes the u-boot won't complain about the firmware
   checksum and it's OK to use now.
3. If you powered off the device before upgrading the sysupgrade.bin, just
   upgrade the factory.bin through the u-boot failsafe interface and then goto
   step 2.

Signed-off-by: Weijie Gao <hackpascal@gmail.com>
[squash commits, use common seama recipes, sync factory image recipe
with ramips version]
Signed-off-by: Mathias Kresin <dev@kresin.me>