etnaviv: rework TS enable to be a derived state

etnaviv: rework TS enable to be a derived state

Draw operations should not use the TS if the TS buffer content is invalid,
as this leads to wrong rendering or even GPU hangs. As the TS valid status
can change between draws (clear operations changing it to valid, blits using
the RS to the color or ZS buffer changing it to invalid), the TS_MEM_CONFIG
must be updated before each draw if the status has changed.

This fixes the remaining TS related piglit failures (regressions of a
standard run against a piglit run with TS completely disabled).

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Reviewed-by: Wladimir J. van der Laan <laanwj@gmail.com>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>