config: use the standard INSTALL_DATA makefile macro

Replace the custom INST makefile macro with the standard
INSTALL_DATA macro for installing and exporting files.

Change-Id: I5d8c41d1c6d2c3ee021e0d6a5fbca8ef9178e74d
Reviewed-on: http://gerrit.openafs.org/10723
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>