at91: add support for sam9x60-ek board

at91: add support for sam9x60-ek board

Add support for SAM9X60-EK board.

Hardware:
- SoC: SAM9X60
- RAM: Winbond W972GG6KB-25 (2Gbit DDR2)
- NAND Flash: Micron MT29F4G08ABAEA
- QSPI Flash: Microchip SST26VF064B
- EEPROM: Microchip 24AA02E48
- SDMMC: One standard 4-bit SD card interface
- USB: two stacked Type-A connectors with power switches, one micro-B
       USB device
- CAN: 2 interfaces (Microchip MCP2542)
- Ethernet: one 10/100Mbps
- WiFi/BT: one optional WiFi/Bluetooth interface
- Audio: one ClassD port
- Display: one 24-bit LCD interface
- Camera: one 12-bit image sensor interface
- IO: one IO expander (Microchip MCP23008)
- Debug ports: one J-Link-OB + CDC, one JTAG interface
- Leds: one RGB LED
- Buttons: 4 push button switches
- Expansion: one PIO connector, one mikrobus connector
- Power management: two power regulators, two power consumption measurement
                    devices

Flashing:
- follow the procedure at [1]

[1] https://www.linux4sam.org/bin/view/Linux4SAM/Sam9x60EKMainPage#Create_a_SD_card_with_the_demo

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