ARM: at91: remove IRQF_DISABLED

This flag is a NOOP since 2.6.36 and can be removed.

This is an update for 3.11 of a patch already sent for 3.10

Signed-off-by: Michael Opdenacker <michael.opdenacker@free-electrons.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>