OvmfPkg/EnrollDefaultKeys: extract MICROSOFT_VENDOR_GUID

OvmfPkg/EnrollDefaultKeys: extract MICROSOFT_VENDOR_GUID

The GUID

  77FA9ABD-0359-4D32-BD60-28F4E78F784B

is specified in MSDN, at
<https://msdn.microsoft.com/en-us/ie/dn932805(v=vs.94)>, therefore it
deserves an entry in the package DEC file, and a header file under
"Include/Guid".

(Arguably, this GUID declaration / definition could even live under
SecurityPkg, but the edk2 tradition has been to hoist GUIDs,
protocols/PPIs, and lib classes from OvmfPkg to a core package only when
dependent C code is added to the core package.)

Cc: Anthony Perard <anthony.perard@citrix.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Julien Grall <julien.grall@arm.com>
Bugzilla: https://bugzilla.tianocore.org/show_bug.cgi?id=1747
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Philippe Mathieu-Daude <philmd@redhat.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Gary Lin <glin@suse.com>