i965: Integrate precise trig into configuration infrastructure

i965: Integrate precise trig into configuration infrastructure

With this change, to enable precise SIN and COS instructions
on Intel hardware, one can put

<option name="precise_trig" value="true"/>

in the proper drirc file.

V2: Make option name more generic

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Stephane Marchesin <stephane.marchesin@gmail.com>