OvmfPkg: Link AuthVariableLib for following merged variable driver deploy

OvmfPkg: Link AuthVariableLib for following merged variable driver deploy

AuthVariableLib and TpmMeasurementLib library classes are now linked with
MdeModulePkg/Universal/Variable/RuntimeDxe/VariableRuntimeDxe.inf
to optionally support secure variables.

For OvmfPkg,
link AuthVariableLib and DxeTpmMeasurementLib in SecurityPkg
when SECURE_BOOT_ENABLE = TRUE,
and link AuthVariableLibNull and TpmMeasurementLibNull in MdeModulePkg
when SECURE_BOOT_ENABLE = FALSE.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Tested-by: Laszlo Ersek <lersek@redhat.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@17760 6f19259b-4bc3-4df7-8a09-765794883524