irq 4 is sharing with idma, after change vuart to level trigger, the idma
driver could handle this irq 4 and send out EOI, which cause the irq storm.
move vuart irq to a not used 6.
Tracked-On: https://github.com/projectacrn/acrn-hypervisor/issues/1476
Signed-off-by: Jason Chen CJ <jason.cj.chen@intel.com>