i965: Update SOL state for Broadwell.

i965: Update SOL state for Broadwell.

Unlike on Gen7, we can directly set the offset via the state packet.
We also -have- to: the kernel SOL reset code won't work anymore.

v2: Fix copy and paste mistake in buffer stride setup; drop stale
    comment (caught by Eric Anholt).  Add a perf_debug for missing
    MOCS setup.

v3: Rebase on Paul Berry's changes to CurrentVertexProgram.

v4: Fix SO Write Offset handling.  We need to set bits 20 and 21 so the
    hardware both loads and saves the offset.  There's also a
    restriction that 3DSTATE_SO_BUFFER can only be programmed once per
    buffer between primitives, so the "reset to zero" code needed
    reworking.  Fixes most of the transform feedback Piglit tests.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net> [v2]