vfio/spapr: Add cond_resched() for huge updates

Clearing very big IOMMU tables can trigger soft lockups. This adds
cond_resched() to allow the scheduler to do context switching when
it decides to.

Signed-off-by: Alexey Kardashevskiy <[e-mail]>
Reviewed-by: David Gibson <[e-mail]>
Signed-off-by: Alex Williamson <[e-mail]>

drivers/vfio/vfio_iommu_spapr_tce.c

···
 	enum dma_data_direction direction;
 
 	for ( ; pages; --pages, ++entry) {
+		cond_resched();
+
 		direction = DMA_NONE;
 		oldhpa = 0;
 		ret = iommu_tce_xchg(tbl, entry, &oldhpa, &direction);