Use BB collections for Aspeed tree patches

Move the Aspeed u-boot tree patches to a directory where they can
be conditionally applied when the Aspeed layer is in the build
configuration.

This is a better way to achieve 273ec60e436 since it enables the Aspeed
BSP layer to name its u-boot/kernel recipes whatever it wants.

Remove stubbed do_configure from u-boot_%.bbappend.  It is no longer
required since the bbappend is only activated when the aspeed layer
and associated u-boot recipes are in the layer configuration.

Tested: Built u-boot recipe for witherspoon and palmetto targets
Change-Id: I52dceb65598e0cf660ad035a8f14e9894325ca71
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/meta-phosphor/conf/layer.conf b/meta-phosphor/conf/layer.conf
index ab0b736..2510f30 100644
--- a/meta-phosphor/conf/layer.conf
+++ b/meta-phosphor/conf/layer.conf
@@ -14,3 +14,10 @@
 
 IMAGE_FEATURES[validitems] += "tools-profile"
 
+# Let us add layer-specific bbappends which are only applied when that
+# layer is included in our configuration
+BBFILES += "${@' '.join('${LAYERDIR}/%s/recipes*/*/*.bbappend' % layer \
+               for layer in BBFILE_COLLECTIONS.split())}"
+# Add layer-specific bb files too
+BBFILES += "${@' '.join('${LAYERDIR}/%s/recipes*/*/*.bb' % layer \
+               for layer in BBFILE_COLLECTIONS.split())}"