[PATCH] swiotlb: cleanup some code duplication cruft

The implementations of swiotlb_sync_single_for_{cpu,device} are
identical. Likewise for swiotlb_syng_sg_for_{cpu,device}. This patch
move the guts of those functions to two new inline functions, and
calls the appropriate one from the bodies of those functions.

Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>