OvmfPkg: resolve TpmMeasurementLib dependency introduced in r14687

(1) OVMF depends on

  MdeModulePkg/Universal/SecurityStubDxe/SecurityStubDxe.inf

unconditionally.

(2) When OVMF is built with -D SECURE_BOOT_ENABLE, then

  SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.inf

is injected into SecurityStubDxe above.

(3) SVN r14687 ("Add TPM2 implementation.") has made
DxeImageVerificationLib dependent on TpmMeasurementLib.

Currently the last link of the

  OVMF -> SecurityStubDxe -> DxeImageVerificationLib -> TpmMeasurementLib

dependency chain is unresolved:

  build.py...
  /.../OvmfPkg/OvmfPkgX64.dsc(...): error 4000: Instance of library class [TpmMeasurementLib] is not found
  in [/.../SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.inf] [X64]
  consumed by module [/.../MdeModulePkg/Universal/SecurityStubDxe/SecurityStubDxe.inf]

Let's provide a library instance for TpmMeasurementLib the same way as
"SecurityPkg/SecurityPkg.dsc" does (SVN r13964.)

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: svn://svn.code.sf.net/p/edk2/code/trunk/edk2/OvmfPkg@14690 6f19259b-4bc3-4df7-8a09-765794883524