ACPI: thinkpad-acpi: use killable instead of interruptible mutexes

Unfortunately, POSIX in all of its braindamage, do not state that userspace has
to deal with EINTR in read/write and friends... so, lesser code just doesn't.

Switch from *_interruptible to *_killable on the sysfs- and procfs-related
mutexes.  This closes this possible can of worms.

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Len Brown <len.brown@intel.com>