i965: Refactor tiled memcpy functions and move them into their own file

i965: Refactor tiled memcpy functions and move them into their own file

This commit refactors the tiled_memcpy code in intel_tex_subimage.c and
moves it into its own file intel_tiled_memcpy files.  Also, xtile_copy and
ytile_copy are renamed to linear_to_xtiled and linear_to_ytiled
respectively.  The *_faster functions are similarly renamed.

There was also a bit of logic to select between the the libc provided
memcpy function and our custom memcpy that does an RGBA -> BGRA swizzle.
This was moved into an intel_get_memcpy function so that rgba8_copy can
live (and be inlined) in intel_tiled_memcpy.c.

v2: Jason Ekstrand <jason.ekstrand@intel.com>
   - Better commit message
   - Fix up the copyright on the intel_tiled_memcpy files
   - Various whitespace fixes
   - Moved a bunch of stuff that did not need to be exposed from
     intel_tiled_memcpy.h to intel_tiled_memcpy.c
   - Added proper documentation for intel_get_memcpy
   - Incorperated the ptrdiff_t tweaks from commit 225a09790

v3: Jason Ekstrand <jason.ekstrand@intel.com>
   - Fixed a comment
   - Move the tile size constants into the .c file

Signed-off-by: Jason Ekstrand <jason.ekstrand@intel.com>
Reviewed-by: Chad Versace <chad.versace@intel.com>