The change is a no-op for existing clients, and it will simplify
adding the support for ECC EKs. The activation code no longer makes
assumptions about EK's type and handle (i.e. RSA and 0x81010001),
and instead relies on TPM.EKs() to provide the EK's details.
This PR adds:
* Renames 'PlatformEK' to 'EK'
* More consistant support of EKs without certificates
* Removes HTTP GET to Intel EK certificate service
* Always populates EK.Public
* Refactor serialized keys into own structure, in preparation for making Key an interface.
* Refactor key logic into separate structures for each platform/TPMversion invariant.
* Implement review feedback
