gallivm: Remove bogus assert.

It is perfectly valid for the swizzle to be bigger than 2. For example the
texel offsets could be

  SAMPLE ..., IMM[0].zzz

What is not correct is for chan_index to be bigger than 2.

Trivial.
gallivm: (trivial) fix using one lod instead of per-quad lod for texel fetch

The logic for choosing number of lods was bogus.
(The code should ultimately handle the case of only one lod even with multiple
quads but currently can't.)
i965: fix alpha test for MRT

Include src0 alpha in the RT write message when using MRT, so it is used
for the alpha test instead of the normal per-RT alpha value.

Fixes broken rendering in Dota2 under Wine [FDO #62647].

No Piglit regressions on Ivybridge.

V2: reuse (and simplify) existing sample_alpha_to_coverage flag in
the FS key, rather than adding another redundant one.

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
Reviewd-by: Paul Berry <stereotype441@gmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=62647
NOTE: This is a candidate for the stable branches.
[RFC] nvc0: implement compute support for nvc0
[RFC] nvc0: implement MP performance counters for nvc0:nvc8
Merge branch 'nvc0_compute' of github.com:hakzsam/mesa into nvc0_compute