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/package/occ/occ.mk b/openpower/package/occ/occ.mk
index 39ad15e..7d8c582 100644
--- a/openpower/package/occ/occ.mk
+++ b/openpower/package/occ/occ.mk
@@ -18,7 +18,7 @@
 
 OCC_IMAGE_BIN_PATH = obj/image.bin
 
-OCC_DEPENDENCIES = host-binutils host-ppe42-gcc
+OCC_DEPENDENCIES = host-binutils host-ppe42-toolchain
 ifeq ($(BR2_OCC_GPU_BIN_BUILD),y)
 	OCC_DEPENDENCIES += hostboot-binaries
 endif