Remove obmc-mrw machine feature

Using MRW or not is distro policy.  As such remove the obmc-mrw
machine feature.

Do not enable the remaining obmc-mrw distro feature in the base
phosphor distro configuration.

Create new distro configs for the systems that use MRW today
(i.e. Witherspoon) that enables the obmc-mrw distro feature and point
the local.conf.sample at the new distro configuration.

Change-Id: If4cedc745b3ee942518fbfd4d5cf2cd5b60f346d
Tested: Built a Witherspoon image and validate the manifest
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/meta-witherspoon/conf/distro/openbmc-witherspoon.conf b/meta-witherspoon/conf/distro/openbmc-witherspoon.conf
new file mode 100644
index 0000000..27bf881
--- /dev/null
+++ b/meta-witherspoon/conf/distro/openbmc-witherspoon.conf
@@ -0,0 +1,2 @@
+require conf/distro/include/phosphor-base.inc
+require conf/distro/include/openpower-mrw.inc