sh: Always fixup unaligned userspace accesses on sh64.

sh64 has traditionally had this configurable via a Kconfig option
(CONFIG_SH64_USER_MISALIGNED_FIXUP). In practice it has never really been
terribly useful to turn this off, so just get rid of the option entirely.

We leave the sysctl around so we don't end up breaking existing root
file systems, and to allow folks that really want this off to do so at
their own risk.

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