meta-openpower: obmc-phosphor-initfs add distro suffix

For obmc-phosphor-initfs, add df-openpower distro suffix to avoid
poisoning other machines or distros using this layer.  This is
effectively bringing this recipe up to the state of other openpower
recipes.

Change-Id: I6a0ad96a38a7968b83174ac3af83b1de18d3c8f3
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/recipes-phosphor/initfs/obmc-phosphor-initfs.bbappend b/recipes-phosphor/initfs/obmc-phosphor-initfs.bbappend
index 283f0b1..bb8a87c 100644
--- a/recipes-phosphor/initfs/obmc-phosphor-initfs.bbappend
+++ b/recipes-phosphor/initfs/obmc-phosphor-initfs.bbappend
@@ -1 +1 @@
-RDEPENDS_${PN} += "cf-fsi-firmware"
+RDEPENDS_${PN}_append_df-openpower = " cf-fsi-firmware"