freedreno/a6xx: limit scratch/debug markers to debug builds

freedreno/a6xx: limit scratch/debug markers to debug builds

The overhead does seem to matter when you have a high enough # of draw
calls that effect few bins/pixels, because these writes would happen
unconditionally (ie. not part of a state-group).

Possibly we could keep these if we moved them into a state-group so the
register writes would be no-ops on bins with no geometry.  OTOH I
usually end up adding in a WFI when using them scratch reg values to
track down a crash.  (So add a WFI to mitigate the annoyance of needing
to use a debug build to get scratch regs to locate the position of a
crash/hang in the cmdstream.)

Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Kristian H. Kristensen <hoegsberg@google.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3435>