ARM: at91: rename defconfig files appropriately

rename all Atmel reference board as soc defconfig

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Cc: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>