etnaviv: Fix rework ZSA into a derived state

In case the stencil is modified, it is also enabled. That was the
behavior of the original code, which was also the correct behavior,
so reinstate the behavior.

Fixes dEQP-GLES2.functional.fragment_ops.depth_stencil.* on STM32MP1 GC400T.

Fixes: b29fe26d438 ("etnaviv: rework ZSA into a derived state")
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Signed-off-by: Marek Vasut <marex@denx.de>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8174>
(cherry picked from commit 33a6c01e12cca60903fb78af44ecca3899ad628f)
2 files changed