UefiCpuPkg: Implement library support for VMGEXIT
    
    BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=2198
    
    To support handling #VC exceptions and issuing VMGEXIT instructions,
    create a library with functions that can be used to perform these
    #VC/VMGEXIT related operations. This includes functions for:
      - Handling #VC exceptions
      - Preparing for and issuing a VMGEXIT
      - Performing MMIO-related write operations to support flash emulation
      - Performing AP related boot opeations
    
    The base functions in this driver will not do anything and will return
    an error if a return value is required. It is expected that other packages
    (like OvmfPkg) will create a version of the library to fully support an
    SEV-ES guest.
    
    Cc: Eric Dong <eric.dong@intel.com>
    Cc: Ray Ni <ray.ni@intel.com>
    Cc: Laszlo Ersek <lersek@redhat.com>
    Reviewed-by: Eric Dong <eric.dong@intel.com>
    Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
    Regression-tested-by: Laszlo Ersek <lersek@redhat.com>