futility: modify private key validation to work for both local and cloud

During GSCVD signing, when validating the platform private key, use
the appropriate methods for accessing the key modulus, depending on
the key location (local vs Cloud KMS).

BRANCH=none
BUG=b:345464956
TEST=validated that RO_GSCVD signing with Cloud KMS based keys works
     as expected.

Change-Id: I3a1d58c0860a9f75600d82d0389db6a606f43968
Signed-off-by: Vadim Bendebury <vbendeb@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/5605263
Reviewed-by: Julius Werner <jwerner@chromium.org>
1 file changed