Use SSE in the softgpu to improve perf

And also reduce threading a bit, improving perf for small triangles.

Star Ocean world: 40% -> 48%
Star Ocean inside: 187% -> 238%
Star Ocean battle: 53% -> 72%
Crisis Core menu: 510% -> 620%
Crisis Core ingame: 124% -> 145%
ClaDun: 95% -> 128%

Only changed parts that seemed relatively stable.

-[Unknown]