serial: 8250_dw: Set port capabilities based on CPR register

The Designware UART has an optional support for 16750
compatible Auto Flow Control. This will enable it based on
the AFCE bit in Component Parameter Register.

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>