ARM: atmel: add sama5d3xek support

Add sama5d3xek support with following feature
  - boot from NAND flash, PMECC support, 4bit ECC @ 512 bytes sector
  - boot from SPI flash support
  - boot from SD card support
  - LCD support
  - EMAC support
  - USB OHCI support

Signed-off-by: Bo Shen <voice.shen@atmel.com>
Signed-off-by: Andreas Bießmann <andreas.devel@googlemail.com>