OvmfPkg/Sec: Add #VC exception handling for Sec phase

OvmfPkg/Sec: Add #VC exception handling for Sec phase

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=2198

An SEV-ES guest will generate a #VC exception when it encounters a
non-automatic exit (NAE) event. It is expected that the #VC exception
handler will communicate with the hypervisor using the GHCB to handle
the NAE event.

NAE events can occur during the Sec phase, so initialize exception
handling early in the OVMF Sec support.

Before establishing the exception handling, validate that the supported
version of the SEV-ES protocol in OVMF is supported by the hypervisor.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Regression-tested-by: Laszlo Ersek <lersek@redhat.com>