mboxd: Enable virtual pnor on witherspoon

Clear the EXTRA_OECONF setting that disables the virtual pnor support
in the default mboxd recipe.

Change-Id: I83cb38dc4d266d6923e340a7495163b4a1a32d59
Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
diff --git a/meta-witherspoon/recipes-phosphor/mboxd/mboxd.bbappend b/meta-witherspoon/recipes-phosphor/mboxd/mboxd.bbappend
index 8b6248a..4139f5e 100644
--- a/meta-witherspoon/recipes-phosphor/mboxd/mboxd.bbappend
+++ b/meta-witherspoon/recipes-phosphor/mboxd/mboxd.bbappend
@@ -1 +1,3 @@
 MBOXD_FLASH_SIZE = "64M"
+
+EXTRA_OECONF := "${@oe_filter_out('enable_virtual_pnor=no', '', d)}"