phosphor-software-manager-mmc: Set optional-images config

Set the optional-images config option to image-hostfw, which is
an image file added to the mmc code update tarball at build time.

This config option enables signature validation on the files
specified if signature validation is enabled and the optional
file exists in the tarball.

Tested: Verified signature validation was run over the
        image-hostfw file.

(From meta-phosphor rev: 7625008312e8ce8db5e3c46b2c890dbe36718c25)

Change-Id: Ifdd5c27b639453cca77d36f1209b50c7efea20ef
Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
diff --git a/meta-phosphor/classes/phosphor-software-manager-mmc.bbclass b/meta-phosphor/classes/phosphor-software-manager-mmc.bbclass
index ca5fca8..f30f0c0 100644
--- a/meta-phosphor/classes/phosphor-software-manager-mmc.bbclass
+++ b/meta-phosphor/classes/phosphor-software-manager-mmc.bbclass
@@ -4,6 +4,7 @@
 
 EXTRA_OEMESON += "-Dactive-bmc-max-allowed=2"
 EXTRA_OEMESON += "-Dmedia-dir='/media'"
+EXTRA_OEMESON += "-Doptional-images='image-hostfw'"
 
 RDEPENDS_phosphor-software-manager-updater-mmc += " \
     gptfdisk \