etnaviv: Fully replicate back stencil config
The blob replicates both the value mask as well as the stencil reference of the back-facing stencil to the front-facing stencil. This fixes the remaining failures in the following dEQPs:
dEQP-GLES2.functional.fbo.render.*_stencil_index8
Fixes: c8ccd639 ("etnaviv: Fix depth stencil ops on GC880/GC2000") Signed-off-by: Marek Vasut marex@denx.de