vc4: Switch to actually generating vertex and fragment shader code from TGSI.

vc4: Switch to actually generating vertex and fragment shader code from TGSI.

This introduces an IR (QIR, for QPU IR) to do optimization on.  It's a
scalar, SSA IR in general.  It looks like optimization is pretty easy this
way, though I haven't figured out if it's going to be good for our weird
register allocation or not (or if I want to reduce to basically QPU
instructions first), and I've got some problems with it having some
multi-QPU-instruction opcodes (SEQ and CMP, for example) which I probably
want to break down.

Of course, this commit mostly doesn't work, since many other things are
still hardwired, like the VBO data.

v2: Rewrite to use a bunch of helpers (qir_OPCODE) for emitting QIR
    instructions into temporary values, and make qir_inst4 take the 4 args
    separately instead of an array (all later callers wanted individual
    args).