Orion: move I/O macros out of orion.h

Move the Orion register accessor macros out of orion.h, to prevent
them from ending up in the decompressor image (Orion uncompress.h
includes orion.h.)  Move them into io.h, which seems a better place
for this kind of stuff.

Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>
Reviewed-by: Tzachi Perelstein <tzachi@marvell.com>
Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Nicolas Pitre <nico@marvell.com>