gallium: Add tgsi_to_nir to get a nir_shader for a TGSI shader.

gallium: Add tgsi_to_nir to get a nir_shader for a TGSI shader.

This will be used by the VC4 driver for doing device-independent
optimization, and hopefully eventually replacing its whole IR.  It also
may be useful to other drivers for the same reason.

v2: Add all of the instructions I was relying on tgsi_lowering to remove,
    and more.
v3: Rebase on SSA rework of the builder.
v4: Use the NIR ineg operation instead of doing a src modifier.
v5: Don't use ineg for fnegs.  (infer_src_type on MOV doesn't do what I
    expect, again).
v6: Fix handling of multi-channel KILL_IF sources.
v7: Make ttn_get_f() return a swizzle of a scalar load_const, rather than
    a vector load_const.  CSE doesn't recognize that srcs out of those
    channels are actually all the same.
v8: Rebase on nir_builder auto-sizing, make the scalar arguments to
    non-ALU instructions actually be scalars.
v9: Add support for if/loop instructions, additional texture targets, and
    untested support for indirect addressing on temps.
v10: Rebase on master, drop bad comment about control flow and just choose
     the X channel, use int comparison opcodes in LIT for now, drop unused
     pipe_context argument..
v11: Fix translation of LRP (previously missed because I mis-translated
     back out), use nir_builder init helpers.
v12: Rebase on master, adding explicit include of mtypes.h to get
     INTERP_QUALIFIER_*
v13: Rebase on variables being in lists instead of hash tables, drop use
     of mtypes.h in favor of util/pipeline.h.  Use Ken's nir_builder
     swizzle and fmov/imov_alu helpers, drop "struct" in front of
     nir_builder, use nir_builder directly as the function arg in a lot of
     cases, drop redundant members of ttn_compile that are also in
     nir_builder, drop some half-baked malloc failure handling.
v14: The indirect uniform src0 should be scalar, not vector (noticed as
     odd by robclark, confirmed by cwabbott).  Apply Ken's review to
     initialize s->num_uniforms and friends, skip ttn_channel for dot
     products, and use the simpler discard_if intrinsic.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org> (v13)
Acked-by: Rob Clark <robclark@freedesktop.org>