arm : Atmel : add at91sam9x5ek board support

Add at91sam9x5ek board support, this board support the following SoCs
  AT91SAM9G15, AT91SAM9G25, AT91SAM9G35, AT91SAM9X25, AT91SAM9X35

Using at91sam9x5ek_nandflash to configure for the board
Now only supports NAND with software ECC boot up

Signed-off-by: Bo Shen <voice.shen@atmel.com>
[move MAINTAINERS entry to right place]
Signed-off-by: Andreas Bießmann <andreas.devel@googlemail.com>