ARM: io: convert ioremap*() to functions

Convert the ioremap*() preprocessor macros to real functions, moving
them out of line.  This allows us to kill off __arm_ioremap(), and
__arm_iounmap() helpers, and remove __arm_ioremap_pfn_caller() from
global view.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>