i965: Add XRGB to intel_texsubimage_tiled_memcpy()

i965: Add XRGB to intel_texsubimage_tiled_memcpy()

MESA_FORMAT_XRGB8888 is equivalent to MESA_FORMAT_ARGB8888 in terms
of storage on the device, so okay to use this optimized copy routine.

This series builds on work from Frank Henigman to optimize the
process of uploading a texture to the GPU. This series adds support for
MESA_XRGB_8888 and full miptrees where were found to be common activities
in the Smokin' Guns game. The issue was found while profiling the app
but that part is not benchmarked. Smokin-Guns uses mipmap textures with
an internal format of GL_RGB (MESA_XRGB_8888 in the driver).

These changes need a performance tool to run against to show how they
improve execution performance for specific texture formats. Using this
benchmark I've measured the following improvement on my Ivybridge
Intel(R) Xeon(R) CPU E3-1225 V2 @ 3.20GHz.

1024x1024 texture size
internal-format	Before (MB/sec)     XRGB (MB/sec)
GL_RGBA		628.15		    627.15
GL_RGB		265.95	 	    456.35

512x512 texture size
internal-format	Before (MB/sec)     XRGB (MB/sec)
GL_RGBA		600.23	  	    597.00
GL_RGB		255.50		    440.62

256x256 texture size
internal-format	Before (MB/sec)     XRGB (MB/sec)
GL_RGBA		489.08		    487.80
GL_RGB		229.03	  	    376.63

Benchmark has been sent to mesa-dev list: teximage

Signed-off-by: Courtney Goeltzenleuchter <courtney@LunarG.com>
Reviewed-by: Chad Versace <chad.versace@linux.intel.com>