demmt: simplify handling of mremap syscall
demmt: move "written regions" struct to "buffer" struct
demmt: internally pass buffer pointer instead of buffer id

Will be needed by future changes. As as side effect it speeds up
demmt a bit, because we don't need to browse the array of possible
buffers when buffer id is unknown.
demmt: add "quiet" option
demmt: track gpu-only buffers
demmt: envydis integration

For now only NVC1_3D/NVC0_M2MF combo is supported.
demmt: output with colors
demmt: parse 2 "new" messages: gpu_map2 and gpu_unmap2