i965: Use unsynchronized maps for the program cache on LLC platforms.

i965: Use unsynchronized maps for the program cache on LLC platforms.

There's no reason to stall on pwrite - the CPU always appends to the
buffer and never modifies existing contents, and the GPU never writes
it.  Further, the CPU always appends new data before submitting a batch
that requires it.

This code predates the unsynchronized mapping feature, so we simply
didn't have the option when it was written.

Ideally, we would do this for non-LLC platforms too, but unsynchronized
mapping support only exists for LLC systems.

Saves a bunch of stall avoidance copies when uploading shaders.

v2: Rebase on changes to previous patch.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Kristian Høgsberg <krh@bitplanet.net> [v1]