platform-drivers: x86: pmic: Restore the dropped buslock/unlock

When I added the buslock/unlock mechanism to the pmic code in order to
get rid of the horrible work queue stuff, stupid me missed to add the
new callbacks to the irq_chip.

In consequence Andrew removed the unused functions, but I missed that.

Add them back and hook them up proper.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Matthew Garrett <mjg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Matthew Garrett <mjg@redhat.com>