at91sam9263: merge all boards defconfig into only one

Tested on at91sam9263ek

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Cc: Guillaume GARDET <guillaume.gardet@free.fr>
Cc: Grégory Hermant <gregory.hermant@calao-systems.com>
Cc: Nicolas Ferre <nicolas.ferre@atmel.com>