ARM: at91: add defconfig to enable DRM on 9x5 and 9n12

Add a defconfig file to enable the DRM support on 9x5 series and 9n12.
DRM support requires CCF which is not available on other ARMv5 devices.
Using CCF with those device leads to compilation errors due to function
redefinitions.

Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>