Integrate openpower-libhei with openpower-hw-diags

Pull down openpower-libhei as a subproject and build the isolator
support into openpower-hw-diags.

Signed-off-by: Ben Tyner <ben.tyner@ibm.com>
Change-Id: I6eeacc802363fec6f0f113e75eb268a8c1774b7c
diff --git a/subprojects/libhei.wrap b/subprojects/libhei.wrap
new file mode 100644
index 0000000..dedce68
--- /dev/null
+++ b/subprojects/libhei.wrap
@@ -0,0 +1,3 @@
+[wrap-git]
+url = https://gerrit.openbmc-project.xyz/openbmc/openpower-libhei
+revision = head