[ARM] 3194/1: add pfn_to_kaddr macro for ARM take2

Patch from Hiroki Kaminaga

This patch defines a new macro: pfn_to_kaddr(pfn).
Same macro is already defined on other arch, such as i386.

Signed-off-by: Hiroki Kaminaga <kaminaga@sm.sony.co.jp>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>