Revert "serial-uartlite: Do not use static struct uart_driver out of probe()"

This reverts commit 3b209d25.

As Johan says, this driver needs a lot more work and these changes are
only going in the wrong direction:
    https://lkml.kernel.org/r/20190523091839.GC568@localhost



Reported-by: Johan Hovold <johan@kernel.org>
Cc: Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>
Cc: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>