OvmfPkg/PlatformPei: clear CPU caches

OvmfPkg/PlatformPei: clear CPU caches

This is for conformance with the TCG "Platform Reset Attack Mitigation
Specification". Because clearing the CPU caches at boot doesn't impact
performance significantly, do it unconditionally, for simplicity's
sake.

Flush the cache on all logical processors, thanks to
EFI_PEI_MP_SERVICES_PPI and CacheMaintenanceLib.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Anthony Perard <anthony.perard@citrix.com>
Cc: Julien Grall <julien.grall@linaro.org>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Tested-by: Anthony PERARD <anthony.perard@citrix.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Regression-tested-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>
[lersek@redhat.com: remove bogus Message-Id line from commit msg]