pkcs7verify: add protocol locate function

Add a function which tries to locate the protocol but then tries to
load the Pkcs7VerifyDxe.efi file to provide it if it's not found.
This allows us to rely on pkcs7verify always being present in the
platform, because we can supply it simply by placing a signed copy
from tianocore in the root directory.

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
3 files changed