serial: 8250_pci: more BayTrail error-free bauds

Support the following additional baud rates with 0% error:
	500000, 1500000, 2500000, 3500000

Signed-off-by: Aaron Sierra <asierra@xes-inc.com>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>