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-witherspoon/conf/machine/witherspoon.conf b/meta-witherspoon/conf/machine/witherspoon.conf
index a3b25fd..fe951e4 100644
--- a/meta-witherspoon/conf/machine/witherspoon.conf
+++ b/meta-witherspoon/conf/machine/witherspoon.conf
@@ -17,6 +17,12 @@
 PHOSPHOR_MRW_URI = "git://github.com/open-power/witherspoon-xml"
 PHOSPHOR_MRW_REV = "d25ba72d544b2878e322421b33a130836619664c"
 
+DISTRO_FEATURES_append = "\
+        obmc-openpower \
+        obmc-openpower-extra \
+        obmc-openpower-legacy \
+        "
+
 # Inhibit phosphor-hwmon-config-mrw
 VIRTUAL-RUNTIME_phosphor-hwmon-config = ""