UEFI related headers were copied from edk2.

A new build option "MK_LOADER_EFI_SECUREBOOT" was added to allow
loading of trusted anchors from UEFI.

Certificate revocation support is also introduced.
The forbidden certificates are loaded from dbx variable.
Verification fails in two cases:

There is a direct match between cert in dbx and the one in the chain.
The CA used to sign the chain is found in dbx.
One can also insert a hash of TBS section of a certificate into dbx.
In this case verifications fails only if a direct match with a
certificate in chain is found.

Submitted by: Kornel Duleba <mindal@semihalf.com>
Reviewed by: sjg
Obtained from: Semihalf
Sponsored by: Stormshield
Differential Revision:	https://reviews.freebsd.org/D19093