HV: disable vuart when dbg uart is disabled

vuart it used for SOS to output log to HV console,
so if dbg uart is disabled, it need be disabled too:
just unregister its PIO.

Tracked-On: 2170
Signed-off-by: Minggui Cao <minggui.cao@intel.com>
Acked-by: Eddie Dong <eddie.dong@intel.com>

hypervisor/debug/uart16550.c

@@ -235,3 +235,8 @@ bool is_pci_dbg_uart(union pci_bdf bdf_value)
 
 	return ret;
 }
+
+bool is_dbg_uart_enabled(void)
+{
+	return uart_enabled;
+}