mesa: fix prog_optimize.c assertions triggered by SWZ opcode

The SWZ instruction can have swizzle terms >4 (SWIZZLE_ZERO, SWIZZLE_ONE).
These swizzle terms caused a few assertions to fail.
This started happening after the commit "mesa: Actually use the Mesa IR
optimizer for ARB programs." when replaying some apitrace files.

A new piglit test (tests/asmparsertest/shaders/ARBfp1.0/swz-08.txt)
exercises this.

Cc: "10.3" <mesa-stable@lists.freedesktop.org>
Reviewed-by: Charmaine Lee <charmainel@vmware.com>
draw: (trivial) remove duplicated lines
vc4: Actually implement VC4_DEBUG=cl.
vc4: Add support for stencil operations.

While depth test state is passed through the fragment shader as sideband,
data, the stencil test state has to be set by the fragment shader itself.

Many tests are still failing, but this gets most of hiz/ passing.