[CORE] vmm_vcpu_irq: Don't depend on return code of VCPU pause/resume APIs

On SMP host, the vmm_manager_vcpu_pause() and vmm_manager_vcpu_resume()
will probably do Async IPIs to pause/resume a VCPU. This means we cannot
rely on the return value of this APIs on SMP host.

This patch makes vcpu_irq_wfi_resume() and vmm_vcpu_irq_wait_timeout()
more suitable for SMP host.

Signed-off-by: Anup Patel <anup@brainfault.org>