tests/gem_tiled_fence_blits: split into subtests
tests/gem_tiled_fence_blits: split into subtests

The gem_tiled_fence_blits test tends to get oom killed
on low memory (< 4GB) Android systems. This is because the
test tries to allocate (sysinfo.totalram * 9 / 10) in
buffer objects and the remaining 10% of memory is not
always enough for the Android system.
As with a similar issue with gem_render_linear_blits,
this problem is resolved by splitting into subtests.
A "basic" subtest uses minimal memory buffers to test
the basic operation, and a "normal" subtest which is
skipped if there is insufficient memory.

I also took the opportunity to cull some numeric literals.

Signed-off-by: Tim Gore <574638b6c8be9618c62b9975be7a73fefbc6d4f1@intel.com>

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