GUID value used for PcdTpmInstanceGuid to indicate TPM is disabled.
Include/Guid/TpmInstance.h

GUID Information

GUID's Guid Name	GUID's Guid
gEfiTpmDeviceInstanceNoneGuid	{ 0x00000000, 0x0000, 0x0000, { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 } }

Refer to Header File