at91: remove not needed depends on

Those "depends on" are a double check as all machine entries are
surrounded by "if <ARCH_xxx>" conditions.

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: Andrew Victor <linux@maxim.org.za>