ibm: witherspoon: Set QB_MACHINE

Witherspoon has a Qemu model called witherspoon-bmc.

Change-Id: I086b350182c0deb990b93d88461162181c29e815
Signed-off-by: Joel Stanley <joel@jms.id.au>
diff --git a/meta-ibm/conf/machine/witherspoon.conf b/meta-ibm/conf/machine/witherspoon.conf
index 947ddf7..b1d9ca2 100644
--- a/meta-ibm/conf/machine/witherspoon.conf
+++ b/meta-ibm/conf/machine/witherspoon.conf
@@ -37,3 +37,6 @@
     "phosphor-fan-control-fan-config"
 
 IMAGE_FEATURES:remove = "obmc-ikvm"
+
+QB_MACHINE:witherspoon = "-machine witherspoon-bmc"
+QB_MEM:witherspoon = "-m 512"