dmar: use spin_lock_irqsave() in qi_submit_sync()

Next patch in the series will use queued invalidation interface
qi_submit_sync() for DMA-remapping aswell, which can be called from interrupt
context.

So use spin_lock_irqsave() instead of spin_lock() in qi_submit_sync().

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Youquan Song <youquan.song@intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>