gettext: install po/Makefile.in.in and config.rpath in gettext-minimal

Some tools that depend on gettext-minimal-native and not gettext-native
now require few more files. Add them to gettext-minimal-native and drop
them from gettext-native.

Signed-off-by: Dmitry Eremin-Solenikov <dmitry_eremin@mentor.com>