fdt: Fix handling of paths with options in them

After syncing the sunxi dts files with the upstream kernel dm/fdt sunxi
builds would no longer boot.

The problem is that stdout-path is now set like this in the upstream dts
files: stdout-path = "serial0:115200n8". The use of options in of-paths,
either after an alias name, or after a full path, e.g. stdout-path =
"/soc@01c00000/serial@01c28000:115200", is standard of usage, but something
which the u-boot dts code so far did not handle.

This commit fixes this, adding support for both path formats.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Simon Glass <sjg@chromium.org>