tty: serial: fsl_lpuart: Add runtime pm support

Add runtime pm support to manage the lpuart clock.

Signed-off-by: Sherry Sun <sherry.sun@nxp.com>
Link: https://lore.kernel.org/r/20221110113859.8485-3-sherry.sun@nxp.com


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