OvmfPkg/Amdsev: Base commit to build encrypted boot specific OVMF

OvmfPkg/Amdsev: Base commit to build encrypted boot specific OVMF

This commit represents the file copied from OvmfPkgX64 with minor
changes to change the build name.

This package will form the basis for adding Sev specific features.
Since everything must go into a single rom file for attestation, the
separated build of code and variables is eliminated.

Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3077
Signed-off-by: James Bottomley <jejb@linux.ibm.com>
Message-Id: <20201130202819.3910-3-jejb@linux.ibm.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@arm.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>