yocto-bsp: generate default properties even if json specified

yocto-bsp: generate default properties even if json specified

Users seem to want to specify incomplete property sets when using json
input.  Allow this by generating default properties before the
user-specified properties are applied; the user will then get the
defaults for any unspecified values, and avoid cryptic backtraces.

(From meta-yocto rev: 3f0361f77cf64844da93ba4a76c42cd5befff5ad)

Signed-off-by: Tom Zanussi <tom.zanussi@intel.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>