kbuild: append git revision for all untagged commits

adds revision suffix for untagged commits that are reachable from a tag

I'm bisecting and don't get the -g...... suffix.  The reason is, that

	git name-rev --tags HEAD

returns e.g.

	HEAD tags/v2.6.17-rc1^0~1067

which is currently good enough for setlocalversion to skip the suffix.
This introduces a dependecy to grep -E, which should be fine.

Signed-off-by: Uwe Zeisberger <zeisberg@informatik.uni-freiburg.de>
Acked-By: Ryan Anderson <ryan@michonline.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>