sh: avoid multiple definition errors with cache funcs

sh: avoid multiple definition errors with cache funcs

Recent builds for SH4 boards fail with a lot of errors like:
	cmd_mem.o: In function 'dcache_invalid_range':
	include/asm/cache.h:25: multiple definition of 'dcache_invalid_range'
	include/asm/cache.h:25: first defined here

This is due to the funcs being defined in the header, but not static
or inline or extern.  So move them to the sh4-specific cache.c file.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>