ibm: Set LAYERSERIES_COMPAT

Starting with sumo, bitbake emits a warning if this variable is
not set.  Indicate sumo branch compatibility.

Change-Id: I592ecf6f9940004b2dccb0f4217464d389c771d4
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/meta-palmetto/conf/layer.conf b/meta-palmetto/conf/layer.conf
index 71cad6d..17780a8 100644
--- a/meta-palmetto/conf/layer.conf
+++ b/meta-palmetto/conf/layer.conf
@@ -7,3 +7,4 @@
 
 BBFILE_COLLECTIONS += "palmetto"
 BBFILE_PATTERN_palmetto = ""
+LAYERSERIES_COMPAT_palmetto = "sumo"