OvmfPkg: add Tcg2PhysicalPresenceLibQemu

OvmfPkg: add Tcg2PhysicalPresenceLibQemu

Cloned "SecurityPkg/Library/DxeTcg2PhysicalPresenceLib" and:

- removed all the functions that are unreachable from
  Tcg2PhysicalPresenceLibProcessRequest() [called from platform BDS],
  or SubmitRequestToPreOSFunction() and
  ReturnOperationResponseToOsFunction() [called from Tcg2Dxe].

- replaced everything that's related to the
  TCG2_PHYSICAL_PRESENCE*_VARIABLE variables, with direct access to
  the QEMU structures.

This commit is based on initial experimental work from Stefan Berger.
In particular, he wrote most of QEMU PPI support, and designed the
qemu/firmware interaction. Initially, Stefan tried to reuse the
existing SecurityPkg code, but we eventually decided to get rid of the
variables and simplify the ovmf/qemu version.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
[lersek@redhat.com: clean up non-idiomatic coding style]
[lersek@redhat.com: null mPpi on invalid PPI address]
Reviewed-by: Laszlo Ersek <lersek@redhat.com>