erlang: install to staging and prune target

Several header files and libraries are needed to compile
erlang applications, so make these available in staging.
Now that they're there, prune out the headers and other
files that were partially present in the target directory.
erlang-rebar: add env for compiling c code
erlang-lager: fix install paths and include

The hrl file needs to be exported and rebar doesn't
like the version number being attached to the install dir
name.
erlang-netlink: new package
new package: erlang-gpio
erlinit: pull in new version for new ERTS
erlang-rebar: reduce verbosity
new package: erlang-nerves
bbberl_defconfig: pull in more erlang modules