softoff: Convert to sdeventplus loop

Tested:
    Builds and passes unit tests

Change-Id: I6c37fa7088b7bcfbfc9f8b93185b826782a72c6a
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/configure.ac b/configure.ac
index 40be188..5cbdfc6 100644
--- a/configure.ac
+++ b/configure.ac
@@ -31,6 +31,9 @@
     AC_MSG_ERROR(["Requires sdbusplus package."]))
 
 AS_IF([test "x$enable_softoff" != "xno"],
+    PKG_CHECK_MODULES([SDEVENTPLUS], [sdeventplus],,\
+        AC_MSG_ERROR(["Requires sdeventplus package."]))
+
     # Check for sdbus++ tool
     [AC_PATH_PROG([SDBUSPLUSPLUS], [sdbus++])]
     AS_IF([test "x$SDBUSPLUSPLUS" == "x"],