i965: Enhance intel_texsubimage_tiled_memcpy() to support all levels

i965: Enhance intel_texsubimage_tiled_memcpy() to support all levels

Support all levels of a supported texture format.

Using 1024x1024, RGBA 8888 source, mipmap
internal-format	Before (MB/sec)     mipmap (MB/sec)
GL_RGBA		627.15		615.90
GL_RGB		456.35		611.53

512x512
GL_RGBA		597.00		619.95
GL_RGB		440.62		611.28

256x256
GL_RGBA		487.80		587.42
GL_RGB		376.63		585.00

Benchmark has been sent to mesa-dev list: teximage_enh

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