at91: add support for sama7g5-ek board

Add support for SAMA7G5-EK board.
Hardware:
- SoC: SAMA7G5
- RAM: Aliance Memory AS4C256M16D3LC (4 Gbit DDR3L)
- SD/MMC: 1 standard 4bit SD Card interface
- USB: 1 Micro-AB host/device, 1 Type-A host, 1 Type-C host
- CAN: 2 interfaces
- Ethernet: 10/100 port, 1Gbps port
- Wi-Fi/BT: 1 optional interface
- Audio: 1 SPDIF RX port, 1 SPDIF TX port, 4 digital microphones
- Camera: 1 RPi CSI camera interface
- Debug: 1 J-Link-OB + CDC, 1 JTAG
- LEDs: 1 RGB
- Buttons: 4 push buttons
- Expansions: 1 RPi Expansion connector, 2 mikroBUS connectors
- Power management: 1 power management IC, 1 power consumption
  measurement device

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>