i965: Generalize sampler state pointer mangling for non-const

i965: Generalize sampler state pointer mangling for non-const

For now, assume that the addressed sampler can be in any of the
16-sampler banks. If we preserved range information this far, we
could avoid emitting these instructions if the sampler were known
to be contained within one bank.

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