Always clamp in ToRGB[A]?()

Before we only clamped with SSE, better to be consistent.

This may also be slightly faster.  I got an inconsistent 1% gain in one area of Senjou no Valkyria 3 (with enough tries I'm convinced it's probably about 1%, sometimes it was more sometimes less.)

I have not tested on ARM but I expect usat to be faster than whatever vfp it was doing for `x > 1.0f ? 1.0f : x`.

Also probably improves softgpu perf a tiny tiny bit, unmeasured.

-[Unknown]