swiotlb: add the late swiotlb initialization function with iotlb memory

swiotlb: add the late swiotlb initialization function with iotlb memory

This enables the caller to initialize swiotlb with its own iotlb
memory late in the bootup.

See git commit eb605a5754d050a25a9f00d718fb173f24c486ef
"swiotlb: add swiotlb_tbl_map_single library function" which will
explain the full details of what it can be used for.

CC: FUJITA Tomonori <[email protected]>
[v1: Fold in smatch warning]
Signed-off-by: Konrad Rzeszutek Wilk <[email protected]>