at91: merge all at91rm9200 defconfig in one single file

About all options present in each file are activated
in the single file.

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