mboxd: convert virtual-pnor to PACKAGECONFIG

Change-Id: Iad65d850e224f9c869a3c14c2698bbb13faa766b
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/meta-phosphor/common/recipes-phosphor/mboxd/mboxd.bb b/meta-phosphor/common/recipes-phosphor/mboxd/mboxd.bb
index 4cb85bb..8915dd7 100644
--- a/meta-phosphor/common/recipes-phosphor/mboxd/mboxd.bb
+++ b/meta-phosphor/common/recipes-phosphor/mboxd/mboxd.bb
@@ -46,6 +46,6 @@
 SYSTEMD_SERVICE_${PN} += "mboxd-reload@.service"
 SYSTEMD_LINK_${PN} += "${@compose_list(d, 'FMT', 'OBMC_CHASSIS_INSTANCES')}"
 
-EXTRA_OECONF = " \
-        enable_virtual_pnor=no \
-        "
+# Disable virtual-pnor by default.
+PACKAGECONFIG ??= ""
+PACKAGECONFIG[virtual-pnor] = "--enable-virtual-pnor,--disable-virtual-pnor"