MLK-17218 tty: serial: imx: add lock for register save/restore

MLK-17218 tty: serial: imx: add lock for register save/restore

The driver save/restore registers in system suspend/resume noirq stage
to support no_console_suspend in power lost case.

In noirq stage with no_console_suspend, .imx_console_write() _maybe_
called to print out log_buf message in .printk() or console_unlock()
called by other drivers.
It should add port.lock to protect the registers save/restore in noirq
stage since .imx_console_write() also access them.

Reported-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Fugang Duan <fugang.duan@nxp.com>