tty: serial: fsl_lpuart: add imx8ulp support

The lpuart of imx8ulp is basically the same as imx7ulp, but it supports
some new features based on imx7ulp, such as it can assert the DMA
request on EOP(end-of-packet).

Here add lpuart support for imx8ulp, and rx_watermark is set to 3 as
imx8ulp RX FIFO depth is 8.

Signed-off-by: Sherry Sun <sherry.sun@nxp.com>
Link: https://lore.kernel.org/r/20230130064449.9564-7-sherry.sun@nxp.com


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