Added new enums for:
- 8/16/32 bit integers
- R, RG, RGB, RGBA
- Normalized and unnormalized

Also fixed FORMAT_LAST.

Change-Id: Ie3eb5286820c44490630e302907350358a1d85dc
Reviewed-on: https://swiftshader-review.googlesource.com/4110Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>