migration/cgs-tdx: add tdx_mig_setup

tdx_mig_setup is assigned to the cgs migration framework's
savevm_state_setup API (invoked on the source side) and loadvm_state_setup
API (invoked on the destination side). The setup work includes:
- create a kvm_device from the tdx-mig driver in KVM. The device fd is
  returned for later communication with the device.
- negotiate with the driver for the size if the memory to map, this
  includes:
  -- KVM_SET_DEVICE_ATTR: sets the configurable attr (only the migration
     buffer size currently) of the device to KVM. The migration flow
     currently finds and send dirty pages one by one, so the migration
     buffer size set to the driver is 4KB (TAGET_PAGE_SIZE);
  -- KVM_GET_DEVICE_ATTR: gets the negotiated kvm_device's attr. This
     obtains from KVM the sizes of the 4 parts (i.e. mbmd buffer size,
     migration buffer size, mac list buffer size, and gpa list buffer
     size) of shared memory.
- map the 4 parts of shared memory.

Signed-off-by: Wei Wang <wei.w.wang@intel.com>

linux-headers/linux/kvm.h

@@ -1511,6 +1511,8 @@ enum kvm_device_type {
 #define KVM_DEV_TYPE_XIVE		KVM_DEV_TYPE_XIVE
 	KVM_DEV_TYPE_ARM_PV_TIME,
 #define KVM_DEV_TYPE_ARM_PV_TIME	KVM_DEV_TYPE_ARM_PV_TIME
+	KVM_DEV_TYPE_TDX_MIG_STREAM,
+#define KVM_DEV_TYPE_TDX_MIG_STREAM	KVM_DEV_TYPE_TDX_MIG_STREAM
 	KVM_DEV_TYPE_MAX,
 };