igt/gem_mmap_wc: Explicitly check for use-after-close
igt/gem_mmap_wc: Explicitly check for use-after-close

We already rely on the mmap(object) surviving close(), but make the test
explicit and early.

Secondly, we don't technically need to call set_domain after writing
through the CPU then reading through WC, since the CPU cache is
consistent for those two paths. Test it.

Signed-off-by: Chris Wilson <711c73f64afdce07b7e38039a96d2224209e9a6c@chris-wilson.co.uk>

tiagovignatti/intel-gpu-tools,mv0/intel-gpu-tools,mv0/intel-gpu-tools,dlespiau/checkmate-test-igt,mv0/intel-gpu-tools,chenxianqin/intel-gpu-tools,dlespiau/checkmate-test-igt,chenxianqin/intel-gpu-tools,dlespiau/checkmate-test-igt,dlespiau/checkmate-test-igt,tiagovignatti/intel-gpu-tools,tiagovignatti/intel-gpu-tools,mv0/intel-gpu-tools,chenxianqin/intel-gpu-tools,chenxianqin/intel-gpu-tools,tiagovignatti/intel-gpu-tools