tests/gem_write_ring_switch: Skip on pre-SNB
tests/gem_write_ring_switch: Skip on pre-SNB

The test requires MI commands only introduced with SNB, and so causes
GPU death on gm45 and ilk.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=66838

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