core: improve of_match_ptr with OF_PLATDATA

Currently of_match_ptr is used to avoid referencing compatible strings
when OF_CONTROL is not enabled. This behaviour could be improved by
taking into account also OF_PLATDATA, as when this configuration is
enabled the compatible strings are not used at all.

Signed-off-by: Walter Lozano <walter.lozano@collabora.com>
Reviewed-by: Simon Glass <sjg@chromium.org>