conf/layer.conf: use BBFILES_DYNAMIC for dynamic layers

The previous code add all BBFILE_COLLECTIONS/recipes*/*/*.bbappend to BBFILES,
which causes the parsing very slow when there are many layers, e.g., I have 87
layers:

* Before:
$ rm -fr tmp-glibc/ cache; time bitbake -p
real    0m45.173s
user    0m0.560s
sys     0m0.060s

* After:
$ rm -fr tmp-glibc/ cache; time bitbake -p
real    0m25.542s
user    0m0.572s
sys     0m0.040s

It wasted 20s which wasn't worth (The host has 128 threads, it should cost more
time on less power host), use BBFILES_DYNAMIC can fix the problem.

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Yi Zhao <yi.zhao@windriver.com>
Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>

conf/layer.conf

@@ -5,10 +5,13 @@ BBPATH .= ":${LAYERDIR}"
 BBFILES += "${LAYERDIR}/recipes-*/*/*.bb \
             ${LAYERDIR}/recipes-*/*/*.bbappend"
 
-# 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())}"
+BBFILES_DYNAMIC += "openembedded-layer:${LAYERDIR}/dynamic-layers/openembedded-layer/*/*/*.bb \
+                    openembedded-layer:${LAYERDIR}/dynamic-layers/openembedded-layer/*/*/*.bbappend \
+                    networking-layer:${LAYERDIR}/dynamic-layers/networking-layer/*/*/*.bb \
+                    networking-layer:${LAYERDIR}/dynamic-layers/networking-layer/*/*/*.bbappend \
+                    virtualization-layer:${LAYERDIR}/dynamic-layers/virtualization-layer/recipes*/*/*.bb \
+                    virtualization-layer:${LAYERDIR}/dynamic-layers/virtualization-layer/recipes*/*/*.bbappend \
+                   "
 
 BBFILE_COLLECTIONS += "selinux"
 BBFILE_PATTERN_selinux = "^${LAYERDIR}/"