xen/arm: drivers: scif: Add support for SCIFA compatible UARTs
For the driver to be able to handle SCIFA interface as well,
this patch just adds the following:
- SCIFA related macros
- New element in "port_params" array to keep SCIFA specific things
- SCIFA compatible string
This patch makes possible to use existing driver for Renesas "Stout"
board based on R-Car H2 SoC (SCIFA).