tests/flip_test: check whether timestamp isn't in the past
tests/flip_test: check whether timestamp isn't in the past

This is mostly useful for when we add support for other clock sources,
e.g. clock_monotic, to check whether the kernel picked the right
clock.

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