distro: Allow other layers to override distro conf

Enable other layers to optionally define a
conf/distro/include/${MACHINE}.conf to override distro
configuration.

Change-Id: I7bc34d4d0d89c0a6568f084c017cd7e9b964ced1
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/conf/distro/openbmc-phosphor.conf b/conf/distro/openbmc-phosphor.conf
index c890d36..b2d207e 100644
--- a/conf/distro/openbmc-phosphor.conf
+++ b/conf/distro/openbmc-phosphor.conf
@@ -39,3 +39,5 @@
 
 # TODO: openbmc/openbmc#12345 - Upgrade to pygobject-3.
 PREFERRED_VERSION_python-pygobject = "2.%"
+
+include conf/distro/include/${MACHINE}.inc