tty: serial: uartlite: Move uart register to probe

Move uart register to probe.
This is in preparation of removing the hardcoding of number of uarts.

Signed-off-by: Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>