sh: Integrate the SH-5 onchip_remap() more coherently.

Presently this is special-cased for early initialization. While there are
situations where these static early initializations are still necessary,
with minor changes it is possible to use this for the regular ioremap
implementation as well. This allows us to kill off the special-casing for
the remap completely and to start tidying up all of the SH-5
special-casing in drivers.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>