tty: serial: uartlite: Prevent changing fixed parameters

This device does not support changing baud, parity, data bits, stop
bits, or detecting breaks. Disable "changing" these settings to prevent
their termios from diverging from the actual state of the uart.

In order to determine the correct parameters to enforce, we read the
various new devicetree parameters to discover how the uart was
configured when it was synthesized. The defaults match
ulite_console_setup. xlnx,use-parity, xlnx,odd-parity, and
xlnx,data-bits are optional since there were in-tree users (and
presumably out-of-tree users) who did not set them.

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Link: https://lore.kernel.org/r/20210826192154.3202269-5-sean.anderson@seco.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>