arm: at91: Add support for gurnard

This board is based on Snapper 9G45 which has an Atmel AT91SAM9G45 chip and
128MB of SDRAM. It includes a small LCD, 2xUSB host, SD card, Ethernet and
two UARTs.

Signed-off-by: Andre Renaud <andre@designa-electronics.com>
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Andreas Bießmann <andreas@biessmann.org>
[apply CONFIG_BOOTDELAY transition]
Signed-off-by: Andreas Bießmann <andreas@biessmann.org>