Support the tablet in (at least) the Toshiba Portege M200 Tablet PC.

This device only appears on the ACPI bus, so isn't caught by the current
entry for it in the uart(4) ISA attachment.

PR:		kern/140172
Reviewed by:	jhb, marcel
Approved by:	ed (mentor)
MFC after:	2 weeks

sys/dev/uart/uart_bus_acpi.c

@@ -59,6 +59,7 @@ static driver_t uart_acpi_driver = {
 static struct isa_pnp_id acpi_ns8250_ids[] = {
 	{0x0005d041, "Standard PC COM port"},		/* PNP0500 */
 	{0x0105d041, "16550A-compatible COM port"},	/* PNP0501 */
+	{0x04f0235c, "Wacom Tablet PC Screen"},		/* WACF004 */
 	{0}
 };