[ARM] Add a common typesafe __io implementation

As Al did for Versatile in 2ad4f86b60b649fd7428265c08d73a3bd360c81b,
add a typesafe __io implementation for platforms to use.  Convert
platforms to use this new simple typesafe implementation.

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