OvmfPkg: make PcdPropertiesTableEnable dynamic

OvmfPkg: make PcdPropertiesTableEnable dynamic

Since PcdPropertiesTableEnable is used by the DXE Core (in the
InstallPropertiesTable() function, which runs at End-of-Dxe), we must also
change the PcdLib class resolution for that module, from the default
BasePcdLibNull to DxePcdLib.

Traditionally we've considered the DXE Core to be incapable of accessing
dynamic PCDs -- the PCD PPI is not available any longer to the DXE Core,
and the PCD Protocol is not available to it *yet*. There are exceptions
however: if the DXE Core can ensure, by whatever means, that the PCD
Protocol *is* available, then DxePcdLib will just work (the latter even
lists DXE_CORE as an allowed client module type). Namely, DxePcdLib looks
up the PCD Protocol dynamically, on the first library call that actually
needs it (for accessing a dynamic PCD); the lookup doesn't occur in a
library constructor.

And because the DXE Core fetches PcdPropertiesTableEnable at End-of-Dxe,
the PCD Protocol is definitely available then.

In addition, we change the default value of PcdPropertiesTableEnable from
the inherited TRUE to FALSE. It makes no difference at this point (our
runtime DXE drivers are not built with the required 4KB section alignment
anyway), but it's better to be clear about this. The properties table
feature requires OS compatibility, and it breaks Windows 7 minimally.
Therefore the default should be FALSE.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Star Zeng <star.zeng@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>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18470 6f19259b-4bc3-4df7-8a09-765794883524