tty: serial: fsl_lpuart: do software reset for imx7ulp and imx8qxp

Do software reset for communication port on imx7ulp and imx8qxp after
the port is registered if the UART controller support the feature.

Do partition reset with LPUART's power on, LPUART registers will
keep the previous status, like on i.MX8QXP platform, which is not
expected action, so need to set the RST bit of GLOBAL register to reset
all uart internal logic and registers.

Currently, only i.MX7ULP and i.MX8QXP LPUART controllers include
global register that support the software reset.

Signed-off-by: Fugang Duan <fugang.duan@nxp.com>
Signed-off-by: Sherry Sun <sherry.sun@nxp.com>
Link: https://lore.kernel.org/r/20210823091801.17447-1-sherry.sun@nxp.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>