genirq: Provide and use __irq_can_set_affinity()

Provide a irq_desc based variant of irq_can_set_affinity() to avoid a
redundant lookup for the core code users.

[ tglx: Split out from combo patch ]

Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --cc kernel/irq/manage.c
Simple merge