ath79: add support for MikroTik RouterBOARD 962UiGS-5HacT2HnT (hAP ac)

ath79: add support for MikroTik RouterBOARD 962UiGS-5HacT2HnT (hAP ac)

This patch adds support for the MikroTik RouterBOARD 962UiGS-5HacT2HnT (hAP ac)

Specifications:
- SoC: QCA9558
- RAM: 128 MB
- Flash: 16 MB SPI
- 2.4GHz WLAN: 3x3:3 802.11n on SoC
- 5GHz WLAN: 3x3:3 802.11ac on QCA9880 connected via PCIe
- Switch: 5x 1000/100/10 on QCA8337 connected via RGMII
- SFP cage: connected via SGMII (tested with genuine & generic GLC-T)
- USB: 1x type A, GPIO power switch
- PoE: Passive input on Ether1, GPIO switched passthrough to Ether5
- Reset button
- "SFP" LED connected to SoC
- Ethernet LEDs connected to QCA8337 switch
- Green WLAN LED connected to QCA9880

Not working:
- Red WLAN LED

Installation:
TFTP boot initramfs image and then perform sysupgrade. Follow common
MikroTik procedure as in https://openwrt.org/toh/mikrotik/common.

Signed-off-by: Ryan Mounce <ryan@mounce.com.au>
(cherry picked from commit c2140e32ce32b9cc60f7d408e20bdf45dce6a634)