lib: libfdt: Add a new API for appending string properties

appendprop is currently appending the source property
to the destination property without removing the NULL
character. This would result in failure while appending
strings. Hence use the new API appendprop_string for
appending string properties.

Change-Id: Ie8243c823b4bdf29a71f3d829495bfabcd2e6f74
2 files changed