meta-intel-openbmc: prep for new override syntax

Ran `scripts/contrib/convert-overrides.py` from upstream Yocto and
fixed up a few by hand that were missed.

Tested: Built s2600wf.

Signed-off-by: Jae Hyun Yoo <jae.hyun.yoo@linux.intel.com>
Change-Id: I983385c8cdd4e2727c5c1a3d56952d6ac7fd89cc
diff --git a/meta-intel-openbmc/meta-s2600wf/recipes-phosphor/skeleton/obmc-libobmc-intf_%.bbappend b/meta-intel-openbmc/meta-s2600wf/recipes-phosphor/skeleton/obmc-libobmc-intf_%.bbappend
index 410b21b..ea01f37 100644
--- a/meta-intel-openbmc/meta-s2600wf/recipes-phosphor/skeleton/obmc-libobmc-intf_%.bbappend
+++ b/meta-intel-openbmc/meta-s2600wf/recipes-phosphor/skeleton/obmc-libobmc-intf_%.bbappend
@@ -1 +1 @@
-FILESEXTRAPATHS_prepend_s2600wf := "${THISDIR}/${PN}:"
+FILESEXTRAPATHS:prepend:s2600wf := "${THISDIR}/${PN}:"