etnaviv: Fix depth stencil ops on GC880/GC2000
This patch fixes depth stencil ops on MX6S GC880 and MX6Q GC2000. The following dEQPs now pass: dEQP-GLES2.functional.fragment_ops.depth_stencil.stencil_depth_funcs.* dEQP-GLES2.functional.fragment_ops.depth_stencil.stencil_ops.* which is roughly 600 fixed dEQP tests.
The problem is that if the front-facing stencil has a value mask 0x00 and the back-facing stencil has some non-zero value mask, then the stencil part of the depth stencil buffer is written with 0x00 unconditionally. The blob replicates the value mask of the back-facing stencil to the value mask of the front-facing stencil to achieve correct rendering, replicate the same behavior here.
Signed-off-by: Marek Vasut marex@denx.de