Add python-protobuf for nanopb

Nanopb depends on python-protobuf to generate codes.

Tested locally by building the image and codes depending on
nanopb.

Signed-off-by: Nan Zhou <nanzhoumails@gmail.com>
Change-Id: Iaaf9cb696a27c4c266d66b9d26ee7e281ebaf810
1 file changed