OvmfPkg: introduce OVMF_PK_KEK1_APP_PREFIX_GUID

OvmfPkg: introduce OVMF_PK_KEK1_APP_PREFIX_GUID

For the EnrollDefaultKeys application, the hypervisor is expected to add a
string entry to the "OEM Strings" (Type 11) SMBIOS table, with the
following format:

4e32566d-8e9e-4f52-81d3-5bb9715f9727:<Base64 X509 cert for PK and first KEK>

The string representation of the GUID at the front is the "application
prefix", in terms of QEMU commit
<https://git.qemu.org/?p=qemu.git;a=commit;h=2d6dcbf93fb0>.

Introduce this GUID in the usual manner.

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>