I/OAT: Rename the source file

Rename the ioatdma.c file in preparation for splitting into multiple files,
which will allow for easier adding new functionality.

Signed-off-by: Shannon Nelson <shannon.nelson@intel.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>