WithSecureBootPolicyProfile should accommodate systems that support timestamp revocation

[chrisccoulson]

WithSecureBootPolicyProfile will generate an incorrect profile on systems that support timestamp revocation (ie, that have a dbt database), not that I've seen any of these devices yet. This is detected explicitly in the new pre-install checks I'm working on, disabling support for WithSecureBootPolicyProfile in this case, but support for dbt should probably be added.

Support for timestamp revocation can be detected from the OsIndicationsSupported global variable, which secboot is already looking at.