at91: USB-A9G20 C01 & C11 board support

Add support for Calao USB-A9G20 boards. It will be integrated in
existing support for board of same form factor using at91sam9260 or
at91sam9263.

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>