gallivm: add fp64 support. (v2.1)

gallivm: add fp64 support. (v2.1)

This adds support for ARB_gpu_shader_fp64 and ARB_vertex_attrib_64bit to
llvmpipe.

Two things that don't mix well are SoA and doubles, see
emit_fetch_double, and emit_store_double_chan in this.

I've also had to split emit_data.chan, to add src_chan,
which can be different for doubles.

It handles indirect double fetches from temps, inputs, constants
and immediates. It doesn't handle double stores to indirects,
however it appears the mesa/st doesn't currently emit these,
it always does UARL/MOV combos, which will work fine.

tested with piglit, no regressions, all the fp64 tests seem to pass.

v2:
switch to using shuffles for fetch/store (Roland)
assert on indirect double stores - mesa/st never emits these (it uses MOV)
fix indirect temp/input/constant/immediates (Roland)
typos/formatting fixes (Roland)

v2.1:
cleanup some long lines, emit_store_double_chan cleanups.

Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>