Comment PI_USM_MIGRATION_TBD0

Author: aidan.belton

sycl/include/CL/sycl/detail/pi.h

@@ -1560,6 +1560,9 @@ typedef enum : pi_bitfield {
   PI_MEM_ALLOC_FLAGS = CL_MEM_ALLOC_FLAGS_INTEL
 } _pi_usm_mem_properties;
 
+// Flag is used for piProgramUSMEnqueuePrefetch. PI_USM_MIGRATION_TBD0 is a
+// placeholder for future developments and should not change the behaviour of
+// piProgramUSMEnqueuePrefetch
 typedef enum : pi_bitfield {
   PI_USM_MIGRATION_TBD0 = (1 << 0)
 } _pi_usm_migration_flags;