The following functions and their related data structures defined in ntrtl.h are kernel mode only functions
RtlInitializeUnicodePrefix
RtlInsertUnicodePrefix
RtlRemoveUnicodePrefix
RtlFindUnicodePrefix
RtlNextUnicodePrefix
RtlDecompressBufferEx2
RtlDecompressFragmentEx
RtlDescribeChunk
RtlReserveChunk
RtlDecompressChunks
RtlCompressChunks
ETA:
RtlFindFirstRunClear
but they are not "marked" as being kernel-mode only.