Updated meta-zepto for scarthgap branch

This layer's sole purpose is simple!
It sets one variable, BBLAYERS_LAYERINDEX_URL, and is sets it to
"https://layers.chxc.se/layerindex/", i.e.
BBLAYERS_LAYERINDEX_URL = "https://layers.chxc.se/layerindex/"
And it does that in order to make use of the Zepto layerindex.

conf/layer.conf

@@ -12,6 +12,6 @@ BBFILE_PRIORITY_zepto := "5"
 LAYERVERSION_zepto = "1"
 LAYERDEPENDS_zepto = "core"
 
-LAYERSERIES_COMPAT_zepto = "kirkstone langdale mickledore nanbield"
+LAYERSERIES_COMPAT_zepto = "scarthgap styhead walnascar"
 
 BBLAYERS_LAYERINDEX_URL = "https://layers.zeptoinitiative.org/layerindex/"