meta-ibm: romulus: override variable assignments

Add overrides to variable assignments as described in "Modify Variables
to Support a Different Machine" in the yocto development tasks manual:
https://www.yoctoproject.org/docs/latest/dev-manual/dev-manual.html#best-practices-to-follow-when-creating-layers

In a nutshell this allows multiple BSP layers to be included
simultaneously in bblayers.conf, which increases the potential for meta
data sharing between layers.

(From meta-ibm rev: 0ccb228f770fe8688fd926ad822244fab6926298)

Change-Id: I4f648d1c2232a6f246b63b8e46731b7ef1af13ac
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/meta-ibm/meta-romulus/recipes-phosphor/packagegroups/packagegroup-obmc-apps.bbappend b/meta-ibm/meta-romulus/recipes-phosphor/packagegroups/packagegroup-obmc-apps.bbappend
index ea1a7e3..920e529 100644
--- a/meta-ibm/meta-romulus/recipes-phosphor/packagegroups/packagegroup-obmc-apps.bbappend
+++ b/meta-ibm/meta-romulus/recipes-phosphor/packagegroups/packagegroup-obmc-apps.bbappend
@@ -1,2 +1,2 @@
-RDEPENDS_${PN}-inventory += " openpower-occ-control phosphor-cooling-type id-button"
-RDEPENDS_${PN}-extras += " phosphor-webui phosphor-image-signing"
+RDEPENDS_${PN}-inventory_append_romulus = " openpower-occ-control phosphor-cooling-type id-button"
+RDEPENDS_${PN}-extras_append_romulus = " phosphor-webui phosphor-image-signing"