tty: serial: fsl_lpuart: don't enable receiver/transmitter before rx/tx dma ready

lpuart32_setup_watermark_enable() will configure the UART FIFO and
watermark, also enable the receiver and transmitter, this should be done
after the rx/tx dma steup ready.

Also add lpuart32_hw_disable() to make sure the receiver/transmitter and
interrupts are disabled during the dma steup.

Signed-off-by: Sherry Sun <sherry.sun@nxp.com>
Link: https://lore.kernel.org/r/20230130054107.9119-1-sherry.sun@nxp.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>