KVM: PPC: Book 3S: XICS: Don't lock twice when checking for resend

KVM: PPC: Book 3S: XICS: Don't lock twice when checking for resend

BugLink: http://bugs.launchpad.net/bugs/1651248
This patch improves the code that takes lock twice to check the resend flag
and do the actual resending, by checking the resend flag locklessly, and
add a boolean parameter check_resend to icp_[rm_]deliver_irq(), so the
resend flag can be checked in the lock when doing the delivery.

We need make sure when we clear the ics's bit in the icp's resend_map, we
don't miss the resend flag of the irqs that set the bit. It could be
ordered through the barrier in test_and_clear_bit(), and a newly added
wmb between setting irq's resend flag, and icp's resend_map.

Signed-off-by: Li Zhong <zhong@linux.vnet.ibm.com>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
(cherry picked from linux-next commit 21acd0e4df04f02176e773468658c3cebff096bb)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>