i965: Split sampler count variable to be per-stage.

i965: Split sampler count variable to be per-stage.

Currently, we only have a single sampler state table shared among all
stages, so we just copy wm.sampler_count into vs.sampler_count.

In the future, each shader stage will have its own SAMPLER_STATE table,
at which point we'll need these separate sampler counts.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Paul Berry <stereotype441@gmail.com>