igt/gem_concurrent_blit: Only read back a few GTT values
igt/gem_concurrent_blit: Only read back a few GTT values

Due to the nature of the test, we can be reasonably sure that it is
either all copied or not. So we can sacrificing testing the entire
buffer for the expected value in order to speed up the test by only
testing along the diagonal.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=84354
Signed-off-by: Chris Wilson <711c73f64afdce07b7e38039a96d2224209e9a6c@chris-wilson.co.uk>

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