serial: 8250_pci: remove exar code

Remove the Exar specific codes from 8250_pci and blacklist those chips
so that the new Exar serial driver binds to the devices.

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Sudip Mukherjee <sudip.mukherjee@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>