Organize OpenPOWER BMC support as features

Add OBMC_MACHINE_FEATURES for OpenPOWER support under openpower.inc.
Select OpenPOWER features in the POWER machines' DISTRO_FEATURES so that
the features are built.

The features are:
  obmc-openpower for required base support
  obmc-openpower-extra for non-essential tools
  obmc-openpower-legacy for deprecated packages like org.openbmc and
    skeleton packages

Part of openbmc/openbmc#2652.

Change-Id: Ib9f44a0c2e243eebb6594de6554cdc3fa0d076af
Signed-off-by: Xo Wang <xow@google.com>
diff --git a/meta-openbmc-machines/meta-openpower/conf/machine/include/openpower.inc b/meta-openbmc-machines/meta-openpower/conf/machine/include/openpower.inc
index cc92027..cbabdbe 100644
--- a/meta-openbmc-machines/meta-openpower/conf/machine/include/openpower.inc
+++ b/meta-openbmc-machines/meta-openpower/conf/machine/include/openpower.inc
@@ -7,6 +7,9 @@
         obmc-host-state-mgmt \
         obmc-chassis-state-mgmt \
         obmc-bmc-state-mgmt \
+        obmc-openpower \
+        obmc-openpower-extra \
+        obmc-openpower-legacy \
         "
 
 VIRTUAL-RUNTIME_skeleton_workbook = "${MACHINE}-config"