arm64: kvm: pmu: Make overflow handler NMI safe

kvm_vcpu_kick() is not NMI safe. When the overflow handler is called by
an NMI, defer waking the vcpu to an irq_work queue.

Signed-off-by: Julien Thierry <julien.thierry@arm.com>
[Small changes to the commit message]
Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
Cc: Christoffer Dall <christoffer.dall@arm.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Suzuki K Pouloze <suzuki.poulose@arm.com>
Cc: kvmarm@lists.cs.columbia.edu