i965: Disassemble sampler message names on Gen5+.

i965: Disassemble sampler message names on Gen5+.

Previously, sampler messages were decoded as

sampler (1, 0, 2, 2) mlen 6 rlen 8              { align1 1H };

I don't know how much time we've collectly wasted trying to read this
format.  I can never recall which number is the surface index, sampler
index, message type, or...whatever that other number is.  Figuring out
the message name from the numerical code is also painful.

Now they decode as:

sampler sample_l SIMD16 Surface = 1 Sampler = 0 mlen 6 rlen 8 { align1 1H };

This is easy to read at a glance, and matches the format I used for
render target formats.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Chris Forbes <chrisf@ijw.co.nz>