freedreno/a6xx: VSC overflow detection/handling

freedreno/a6xx: VSC overflow detection/handling

Check VSC_SIZE/VSC_SIZE2 regs from cmdstream to detect overflow, and
skip use of VSC visibility stream when overflow is detected, to avoid
GPU hangs.  This is done w/ introduction of some CP_REG_TEST/
CP_COND_REG_EXEC packet pairs.

In addition, eventually (after a frame or two) detect the condition and
resize the VSC buffers until overflow no longer happens.

Note that this significantly reduces the initial size of the VSC
buffers, backing out a previous hack to make them 16x larger than
what should be typically required (the previous "solution" for
VSC overflow).

Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Eric Anholt <eric@anholt.net>