OvmfPkg/AcpiPlatformDxe: Check PcdConfidentialComputingGuestAttr
    
    PcdConfidentialComputingGuestAttr can be used to check the cc guest
    type, including td-guest or sev-guest. CcProbe() can do the same
    thing but CcProbeLib should be included in the dsc which uses
    AcpiPlatformDxe. The difference between PcdConfidentialComputingGuestAttr
    and CcProbe() is that PcdConfidentialComputingGuestAttr cannot be used
    in multi-processor scenario but CcProbe() can. But there is no such
    issue in AcpiPlatformDxe.
    
    So we use PcdConfidentialComputingGuestAttr instead of CcProbeLib so that
    it is simpler.
    
    Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
    Cc: Erdem Aktas <erdemaktas@google.com>
    Cc: James Bottomley <jejb@linux.ibm.com>
    Cc: Jiewen Yao <jiewen.yao@intel.com>
    Cc: Gerd Hoffmann <kraxel@redhat.com>
    Cc: Tom Lendacky <thomas.lendacky@amd.com>
    Signed-off-by: Min Xu <min.m.xu@intel.com>