gem_concurrent_blit: Purge the child bufmgr's cache
gem_concurrent_blit: Purge the child bufmgr's cache

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=68169

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