tty: serial: altera_uart: Add devicetree support

With the recent switch of the (currently still out-of-tree) Nios2 Linux
port to devicetree we want to be able to retrieve the resources and
properties from dts.

The old method to retrieve resources and properties from platform data
is still supported.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>