vpnor: Add option to sign squashfs PNOR image

Add option flag to sign the squashfs PNOR image with a private key,
this key can be specified by setting the PRIVATE_KEY_PATH environment
variable prior to building op-build.

Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
diff --git a/openpower/package/openpower-vpnor/openpower-vpnor.mk b/openpower/package/openpower-vpnor/openpower-vpnor.mk
index 257fb70..6a6cdff 100644
--- a/openpower/package/openpower-vpnor/openpower-vpnor.mk
+++ b/openpower/package/openpower-vpnor/openpower-vpnor.mk
@@ -4,7 +4,7 @@
 #
 ################################################################################
 
-HOST_OPENPOWER_VPNOR_VERSION ?= 0e30f86cb44f3ab0aa4080faf32eb4bf2a9b12b2
+HOST_OPENPOWER_VPNOR_VERSION ?= 643e730e3b9818bdd878eebee209b268c234fc65
 HOST_OPENPOWER_VPNOR_SITE ?= $(call github,openbmc,openpower-pnor-code-mgmt,$(HOST_OPENPOWER_VPNOR_VERSION))
 HOST_OPENPOWER_VPNOR_DEPENDENCIES = host-squashfs host-libflash