sign_uefi: Use the v2 crdyshim key for signing crdyboot

Note that this will have no immediate effect on the reven board because
the `crdyboot_presigned` USE flag is set, so these signing operations
are skipped for now.

BRANCH=None
BUG=b:421963848
TEST=make runtests
TEST=create image with dev version of crdyshim
TEST=crdyshim must include the changes from chromium:7416135
TEST=scripts/image_signing/sign_official_build.sh recovery \
TEST=    disk.unsigned tests/devkeys disk.signed
TEST=boot, verify crdyshim successfully verifies the signature

Change-Id: I93af7f6edf44e09a8394353af344a48e6d5a038d
Signed-off-by: Nicholas Bishop <nicholasbishop@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/7427950
Reviewed-by: Benjamin Shai <bshai@google.com>