tty: serial: fsl_lpuart: don't break the on-going transfer when global reset

lpuart_global_reset() shouldn't break the on-going transmit engine, need
to recover the on-going data transfer after reset.

This can help earlycon here, since commit 60f36172 ("serial:
fsl_lpuart: Reset prior to registration") moved lpuart_global_reset()
before uart_add_one_port(), earlycon is writing during global reset,
as global reset will disable the TX and clear the baud rate register,
which caused the earlycon cannot work any more after reset, needs to
restore the baud rate and re-enable the transmitter to recover the
earlycon write.

Also move the lpuart_global_reset() down, then we can reuse the
lpuart32_tx_empty() without declaration.

Fixes: bd5305dc

 ("tty: serial: fsl_lpuart: do software reset for imx7ulp and imx8qxp")
Signed-off-by: Sherry Sun <sherry.sun@nxp.com>
Link: https://lore.kernel.org/r/20221024085844.22786-1-sherry.sun@nxp.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>