Blackfin: pm: drop irq save/restore in standby and suspend to mem callback

Since linux-2.6.31, the kernel suspend framework will do disable_irq/enable_irq,
so save/restore irq in standby and suspend to mem callback should be dropped.
Otherwise the common code notices things are enabled and complains.

Signed-off-by: Steven Miao <realmz6@gmail.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>