m68k: runtime patching infrastructure

Add the basic infrastructure to allow runtime patching of kernel and modules
to optimize a few functions with parameters, which are only calculated once
during bootup and are otherwise constant.  Use this for the conversion between
virtual and physical addresses.

Signed-off-by: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>