tty: serial: define UART_LCR_WLEN() macro

Define a generic UART_LCR_WLEN() macro with a size argument. It can be
used to encode byte size into an LCR value. Therefore we can use it to
simplify the drivers using tty_get_char_size() in the next patches.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20220224095558.30929-1-jslaby@suse.cz


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>