Implement GL_GENERATE_MIPMAP.

Bug 21278131

Change-Id: I6252b84f0fd810496475a6e19c9f131bb69d977f
Reviewed-on: https://swiftshader-review.googlesource.com/3194
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Nicolas Capens <capn@google.com>
3 files changed