Add DTC release version information.

Adopted the version information and implementation
from of the Linux Kernel Makefiles.

Signed-off-by: Jon Loeliger <jdl@jdl.com>

scripts/setlocalversion

@@ -0,0 +1,22 @@
+#!/bin/sh
+# Print additional version information for non-release trees.
+
+usage() {
+	echo "Usage: $0 [srctree]" >&2
+	exit 1
+}
+
+cd "${1:-.}" || usage
+
+# Check for git and a git repo.
+if head=`git rev-parse --verify HEAD 2>/dev/null`; then
+	# Do we have an untagged version?
+	if git name-rev --tags HEAD | grep -E '^HEAD[[:space:]]+(.*~[0-9]*|undefined)$' > /dev/null; then
+		printf '%s%s' -g `echo "$head" | cut -c1-8`
+	fi
+
+	# Are there uncommitted changes?
+	if git diff-index HEAD | read dummy; then
+		printf '%s' -dirty
+	fi
+fi