Revert "s390/pci: remove bit_lock usage in interrupt handler"

This reverts commit 9594ca6b

.

With the handle_simple_irq irq_flow_handler it must be ensured to
not call generic_handle_irq with the same IRQ number on 2 CPUs at
the same time (interrupts are floating on s390).
Contrary to my initial investigation the irq_desc's lock usage in
handle_simple_irq does not ensure this. Thus re-introduce the bit-
lock usage in s390's pci handler.

Reported-by: Ursula Braun <ubraun@linux.ibm.com>
Reported-by: Alexander Schmidt <alexs@linux.ibm.com>
Signed-off-by: Sebastian Ott <sebott@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>