i965/blorp/gen8: Fix blitting of interleaved msaa surfaces
i965/blorp/gen8: Fix blitting of interleaved msaa surfaces

Fixes ES31-CTS.gtf.GL31Tests.texture_stencil8.texture_stencil8_multisample.

Current logic divides given layer of one by number of samples (four)
trashing the layer to zero. Layer adjustment is only to be used with
non-interleaved msaa surfaces where samples for particular layer are
in multiple slices.

I copy-pasted a bit of documentation from
brw_blorp.c::brw_blorp_compute_tile_offsets().

Also took the opportunity to fix the comment regarding sampling
as 2D, cube textures are the only exception.

Reviewed-by: Kenneth Graunke <bd2562f754ec92342f93f61c25d731e290a2ffa8@whitecape.org>
Signed-off-by: Topi Pohjolainen <749697f19798b7f640b17221fd283b903825f071@intel.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler