Create virtual packages for OpenPower toolchain

Create a "toolchain" category, plus "p8-pore-toolchain" and
"ppe42-toolchain" virtual-packages, with the goal of lowering the
coupling between these toolchain and target packages.

Signed-off-by: Klaus Heinrich Kiwi <klaus@linux.vnet.ibm.com>
diff --git a/openpower/Config.in b/openpower/Config.in
index b6decad..412dedb 100644
--- a/openpower/Config.in
+++ b/openpower/Config.in
@@ -1,6 +1,7 @@
 menu "OpenPower"
 
 source "$BR2_EXTERNAL_OP_BUILD_PATH/platform/Config.in"
+source "$BR2_EXTERNAL_OP_BUILD_PATH/toolchain/Config.in"
 
 menu "OpenPower Packages"
 if BR2_OPENPOWER_PLATFORM