irqchip/gic-v3-its: Make its_lock a raw_spin_lock_t

[ Upstream commit c7a3334c762a9b1dd2e39cb2ded00ce66e8a06d1 ]

The its_lock lock is held while a new device is added to the list and
during setup while the CPU is booted. Even on -RT the CPU-bootup is
performed with disabled interrupts.

Make its_lock a raw_spin_lock_t.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>