fdt: don't set linux,phandle

fdt: don't set linux,phandle

This has been deprecated for over 10 years and everything now uses the
plain "phandle" property in preference.  There's no need to set
linux,phandle when creating phandles for nodes that do not have one.

dtc changed the default to creating just phandle in version 1.4.5
released in September 2017 with the justification that the new style had
already been supported for 7 years by that point (see dtc commit 0016f8c
("dtc: change default phandles to ePAPR style instead of both")).

Signed-off-by: John Keeping <john@metanate.com>