adminutil: parallel build fixes

Rearrange the Makefile to make it more parallel build proof.
Add some dependencies on the header files, and avoid rules
with 2 targets.

Reviewed-on: http://gerrit.openafs.org/4497
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit c721bff5035b6e2d87e10be0f4711133b33dc5dc)

Change-Id: Id66cd9557696224a6555f2ceb534fd27794f990a
Reviewed-on: http://gerrit.openafs.org/10309
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>