KVM: x86: split kvm_vcpu_ready_for_interrupt_injection out of dm_request_for_irq_injection

This patch breaks out a new function kvm_vcpu_ready_for_interrupt_injection.
This routine encapsulates the logic required to determine whether a vcpu
is ready to accept an interrupt injection, which is now required on
multiple paths.

Reviewed-by: Steve Rutherford <srutherford@google.com>
Signed-off-by: Matt Gingell <gingell@google.com>
Fixes: 1c1a9ce9
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>