[Blackfin] arch: fix bug - linux-2.6.24 (delayed) disable IRQ feature not functional for handle_simple_irq

Bypass delayed disable feature by implementing chip->disable and
chip->enable.

http://lkml.org/lkml/2008/2/19/115Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Bryan Wu <cooloney@kernel.org>