mmt_bin_decode: reduce code duplication

... and fix 2 bugs (handling of mmt_nvidia_memory_dump and
mmt_nvidia_call_method_data)
Update .gitignores
demmt: dedma replacement

It:
- parses mmt binary format
- inspects all buffers
- keeps content of all buffers in memory
- tracks where application has written to
- buffers all writes (flushes on ioctl or write to another buffer)

- does not support mmt text format
- does not support renouveau traces (does anyone use it?)