i965: Always use CPU mappings for BOs on LLC platforms.
i965: Always use CPU mappings for BOs on LLC platforms.

It looks like there's no big difference for write-only workloads, but
using a CPU map means that if they happen to read without having set the
MAP_READ_BIT, they get 100x the performance for those reads.

Reviewed-by: Kenneth Graunke <bd2562f754ec92342f93f61c25d731e290a2ffa8@whitecape.org>

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