The master irq control in DE must be disabled before irq handling,
and enable after the process. This fixes the irq stall issue on
Ironlake.

Cc: Stable Team <stable@kernel.org>
Signed-off-by: Zou, Nanhai <nanhai.zou@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Eric Anholt <eric@anholt.net>