libefivar: Add Display Only format for Hard Drive

Ref: UEFI Specification Version 2.1 (Errata D) (released October 2008)

Reviewed by: imp, emaste
Approved by: emaste (mentor)
Obtained from: https://github.com/tianocore/edk2/commit/9e6537469d4700d9d793ee21e9c2f2e7ddbb2176
Differential Revision: https://reviews.freebsd.org/D49060