etnaviv: dirty TS state when framebuffer has changed

When switching between framebuffers with and without TS, the TS state
needs to be flushed to the command stream even if the derived state
isn't changed.

Fixes: 4ee7c2c2 ("etnaviv: enable TS, but disable autodisable")
Cc: mesa-stable@lists.freedesktop.org
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>
(cherry picked from commit 29a0ea69)