Implement glShadeModel() for OpenGL ES 1.1.

Change-Id: I9b360f92c0b93a854abfd686cdcdd9b2a1dd6a13
Reviewed-on: https://swiftshader-review.googlesource.com/2700
Tested-by: Nicolas Capens <capn@google.com>
Reviewed-by: Greg Hartman <ghartman@google.com>
Tested-by: Greg Hartman <ghartman@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>