intel/dump_gpu: further track mapping of BOs

We can go further in tracking what BOs are written to by the driver by
tracking when a buffer in unmapped. A BO could be mmap, written, unmap
and never be written to again. In such case we can just write the BO's
content on the first exec buf after unmap and never write it again.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/2201>