i965: Support 32 texture image units on Haswell+.

i965: Support 32 texture image units on Haswell+.

The Intel closed source OpenGL driver recently began supporting 32
texture image units on Haswell.  This makes the open source driver
support 32 as well.

Earlier generations don't have the message header field required to
support more than 16 sampler states, so we continue to advertise 16
there.

On Haswell, this causes us to advertise:
- GL_MAX_TEXTURE_IMAGE_UNITS = 32
- GL_MAX_VERTEX_TEXTURE_IMAGE_UNITS = 32
- GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS = 96
instead of the old values of 16, 16, and 48.

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