asterisk-13.x: Store headers for chan-lantiq

asterisk-13.x: Store headers for chan-lantiq

Store asterisk headers in $(DL_DIR) so chan-lantiq can access them
during the target specific build phase. The headers are tarred up for
"mips_24kc" only because that is currently the only used arch for all
chan-lantiq targets.

Store one archive for each combination of asterisk version (e.g. 13) and
branch (using $(VERSION_NUMBER)). The latter makes sure that a release
build doesn't overwrite the header archive of a master snapshot build
and vice vera.

Signed-off-by: Sebastian Kemper <sebastian_ml@gmx.net>