ACPI: SBS: fix initialization, sem2mutex

cm_sbs_sem is being downed (via acpi_ac_init->acpi_lock_ac_dir) before it is
initialised, with grave results.

- Make it a mutex

- Initialise it

- Make it static

- Clean other stuff up.

Thanks to Paul Drynoff <pauldrynoff@gmail.com> for reporting and testing.

Cc: Rich Townsend <rhdt@bartol.udel.edu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Len Brown <len.brown@intel.com>