softirq: move softirq from hv_main to interrupt context

softirq shouldn't be bounded to vcpu thread. One issue for this
is shell (based on timer) can't work if we don't start any guest.

This change also is trying best to make softirq handler running
with irq enabled.

Also update the irq disable/enabel in vmexit handler to align
with the usage in vcpu_thread.

Tracked-On: #3387
Signed-off-by: Yin Fengwei <fengwei.yin@intel.com>
Acked-by: Anthony Xu <anthony.xu@intel.com>

hypervisor/arch/x86/irq.c

@@ -361,6 +361,8 @@ void dispatch_interrupt(const struct intr_excp_ctx *ctx)
 	} else {
 		handle_spurious_interrupt(vr);
 	}
+
+	do_softirq();
 }
 
 void dispatch_exception(struct intr_excp_ctx *ctx)