Line support for saturating sub

[torsteingrindvik]

I have a kernel operating on lines where I'd like to be able to do a saturating sub.

Support for this would be great.

In my particular case I would:

• Do a saturating sub on u16 operands
• Cast line to f16

Without saturating sub support I think I will need to

• Cast line to f16
• Sub
• Clamp

Which I think is likely to be a bit slower.

[torsteingrindvik]

I realize this isn't supported by non-lined primitives as well atm.