serial: zynq: Add support for serial parameters

serial: zynq: Add support for serial parameters

This adds serial parameters that include stop bit mode, parity mode,
and character length. Mark parity and space parity modes are not
supported.

At the moment, the only path to call setconfig directly is DM testing,
however, this affects the size of SPL for DM testing, so it doesn't
apply to SPL.

Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>