Simplify int4 and float4 types.

Change-Id: Id0d55c1364fc3db05821eb6ef666aed8c5713e31
Reviewed-on: https://swiftshader-review.googlesource.com/3503
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Nicolas Capens <capn@google.com>