Add support for PB_ENABLE_MALLOC in nanopb-c

There will be two version of the the nanopb-c library,
libnanopb-c-2.8.0 which doesn't support automatic malloc
and libnanopb-c-2.8.0-enable_malloc which does.

There will be two version of the the nanopb-c library,
libnanopb-c-2.8.0 which doesn't support automatic malloc
and libnanopb-c-2.8.0-enable_malloc which does.

Set LOCAL_PROTO_OPTIMIZE_TYPE=nanopb-c which doesn't support
malloc and set it to nanopb-c-enable_malloc which does.

For client code details see nanopb-api:
  http://koti.kapsi.fi/jpa/nanopb/docs/reference.html

Change-Id: If238412463aabb5e1d556dfc9c464bcaf9e3333a