witherspoon: Enable BMC signature verification

Enable signature verification in the phosphor-software-manager code
for witherspoon. This causes an error to be logged if updating to
an unsigned image, or image signed with a different key than the one
on the system, and if field mode is set, it'll stop the activation
process.

Tested: Signature verification is enforced on witherspoon,
verified error is logged with and without field mode enabled, and
activation is prevented with field mode enabled.

Change-Id: Ifc8f8054f8d852cc16942af9cbf58d60aff3fc33
Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
1 file changed