overlay: move all additions into separate overlay-omni dir

Change-Id: I851163993992ed06c1cb9470cbd37092a9841ab3
diff --git a/device-omni.mk b/device-omni.mk
index 74e15bc..a99c931 100644
--- a/device-omni.mk
+++ b/device-omni.mk
@@ -1,3 +1,5 @@
+DEVICE_PACKAGE_OVERLAYS += device/google/gs101/overlay-omni
+
 # EUICC
 PRODUCT_PACKAGES += \
     EuiccSupportPixelOverlay
\ No newline at end of file