tty: serial: fsl_lpuart: add LS1028A support

The LS1028A uses little endian register access and has a different FIFO
size encoding.

Signed-off-by: Michael Walle <michael@walle.cc>
Link: https://lore.kernel.org/r/20200306214433.23215-4-michael@walle.cc


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