swiotlb: change swiotlb_bus_to[phys,virt] prototypes

Add a hwdev argument that is needed on some architectures
in order to access a per-device offset that is taken into
account when producing a physical address (also needed to
get from bus address to virtual address because the physical
address is an intermediate step).

Also make swiotlb_bus_to_virt weak so architectures can
override it.

Signed-off-by: Becky Bruce <beckyb@kernel.crashing.org>
Acked-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Cc: jeremy@goop.org
Cc: ian.campbell@citrix.com
LKML-Reference: <1239199761-22886-8-git-send-email-galak@kernel.crashing.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>