introduce generic header file for the software IO/TLB

A series of patches introduce a generic header file for the software
IO/TLB implementation in lib/swiotlb.c.  Currently each architecture using
this code defines the prototypes itself.  The prototypes are moved to
include/linux/swiotlb.h and this file is included in architecture specific
code for X86 and IA64.

This patch:

Create include/linux/swiotlb.h file which contains all function prototypes
for the lib/swiotlb.c file.

(akpm: the dependent patches will be trickled through arch trees)

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "Luck, Tony" <tony.luck@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>