i965: add initial implementation of on disk shader cache

i965: add initial implementation of on disk shader cache

This uses the Mesa disk_cache support to write out the final linked
binary for vertex and fragment shader programs.

This is based off the initial implementation done by Carl Worth. It
has been significantly reworked, first by Tim Arceri, and then by
Jordan Justen.

v2:
 * Squash 'i965: add image param shader cache support'
 * Squash 'i965: add shader cache support for pull param pointers'
 * Sustantially simplified by a rework on top of Jason's 2975e4c56a7a.
 * Rename load_program_data to read_program_data. (Jason)

v3:
 * Simplify and align program read/write. (Jason)

v4:
 * Don't save prog_data size since we know it from the stage. (Ken)
 * Don't save program size, since prog_data includes the size. (Ken)
 * Remove `assert` that potentially could be triggered by disk
   corruption of the cache entries. (Ken)
 * Fix compute shader scratch allocation. (Ken)
 * Remove special case mapping for non-LLC. (Ken)
 * Remove SET_UPLOAD_PARAMS macro

[jordan.l.justen@intel.com: *_cached_program => brw_disk_cache_*_program]
[jordan.l.justen@intel.com: brw_shader_cache.c => brw_disk_cache.c]
[jordan.l.justen@intel.com: don't map to write program when LLC is present]
[jordan.l.justen@intel.com: set program_written_to_cache on read from cache]
[jordan.l.justen@intel.com: only try cache when status is linking_skipped]
[jordan.l.justen@intel.com: all v2-v4 changes noted above]
Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>