Add Merisc board support

Merisc is the family name for a range of AVR32-based boards.

The boards are designed to be used in a man-machine interfacing
environment, utilizing a touch-based graphical user interface. They host
a vast range of I/O peripherals as well as a large SDRAM & Flash memory
bank.

For more information see: http://www.martinsson.se/merisc

Signed-off-by: Jonas Larsson <jonas.larsson@martinsson.se>
Signed-off-by: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>