irq/matrix: Split out the CPU selection code into a helper

irq/matrix: Split out the CPU selection code into a helper

[ Upstream commit 8ffe4e61c06a48324cfd97f1199bb9838acce2f2 ]

Linux finds the CPU which has the lowest vector allocation count to spread
out the non managed interrupts across the possible target CPUs, but does
not do so for managed interrupts.

Split out the CPU selection code into a helper function for reuse. No
functional change.

Signed-off-by: Dou Liyang <douly.fnst@cn.fujitsu.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: hpa@zytor.com
Link: https://lkml.kernel.org/r/20180908175838.14450-1-dou_liyang@163.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>