freedreno/a6xx: add support for ARB_shader_stencil_export
Copied from Turnip.
There are no CTS tests and only two piglit:
glsl-fs-shader-stencil-export
fbo-depth-array
Copied from Turnip.
There are no CTS tests and only two piglit:
glsl-fs-shader-stencil-export
fbo-depth-array