drivers: serial: convert Zephyr constants to rpi-hal constants
drivers: serial: convert Zephyr constants to rpi-hal constants

rpi-hal function "uart_set_format" expects data width in the range
of 5..8. So I created a new function “uart_rpi_set_format” which
contains common parts of “uart_rpi_configure”.

Signed-off-by: Jan Hilsdorf <83466a1871d72c252c7658b05dc1aedc92e8ca55@gmail.com>

zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr