ath79: add support for Aerohive HiveAP 121

ath79: add support for Aerohive HiveAP 121

This commit adds support for the Aerohive HiveAP-121. It was previously
already supported in the ar71xx subtarget.

The following is copied from the commit which added ar71xx support:

Specification:
- SoC: Atheros AR9344-BC2A at 560MHz
- WiFi 1: 2.4GHz Atheros AR9340? - SoC
- WiFi 2: 5.0GHz Atheros AR9382-AL1A
- Memory: 128MB from 2x Nanya NT5TU32M16DG-AC
- SPI: 1MB Macronix MX25L8006E
- NAND: 128MB Hynix H27U1G8F2BTR-BC
- Ethernet: Atheros AR8035-A
- USB: 1x 2.0
- TPM: Atmel SC3204

Flashing:
1. Hook into UART (9600 baud) and enter U-Boot. You may need to enter
a password of administrator or AhNf?d@ta06 if prompted.
2. Once in U-Boot, download and flash LEDE factory image over tftp:

dhcp;
setenv serverip tftp-server-ip;
tftpboot 0x81000000 lede-ar71xx-nand-hiveap-121-squashfs-factory.bin;
nand erase 0x800000 0x800000;
nand write 0x81000000 0x800000 0x800000;
reset;

Signed-off-by: David Bauer <mail@david-bauer.net>