toshiba.h: hide a function prototypes behind __KERNEL__ macro

Currently, tosh_smm() prototype is present in a header file exported to
userland.  This patch fixes it.

Signed-off-by: Alexander Shishkin <virtuoso@slind.org>
Cc: Jonathan Buzzard <jonathan@buzzard.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>