OvmfPkg: disable PcdHiiOsRuntimeSupport

OvmfPkg: disable PcdHiiOsRuntimeSupport

Edk2 commit 8a45f80edad4 ("MdeModulePkg: Make HII configuration settings
available to OS runtime") implements the optional UEFI feature described
in "31.2.11.1 OS Runtime Utilization" in UEFI v2.6.

While this feature might show benefits down the road even in QEMU virtual
machines, at the moment it only presents drawbacks:
- it increases the EfiRuntimeServicesData footprint,
- it triggers HII compatibility problems between edk2 and external drivers
  unconditionally, even if the end-user is not interested in HII and/or in
  configuring said drivers (see
  <https://www.redhat.com/archives/vfio-users/2016-March/msg00153.html>
  and <http://thread.gmane.org/gmane.comp.bios.edk2.devel/9894> for an
  example).

While the feature was being introduced, popular demand for a controlling
Feature PCD rose (see
<http://thread.gmane.org/gmane.comp.bios.edk2.devel/7626>), which is why
we can set it now to FALSE.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>