tty/serial: atmel_serial: auto-enumerate ports

If no platform data provided to enumerate ports, use a bit field
to choose port number and check if port is already initialized.
Use this mechanism for both console and plain serial ports.

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>