st/nine: for clarity, use int32_t instead of int for ps and vs integer constants

Signed-off-by: Axel Davy <axel.davy@ens.fr>
st/nine: Little rework of boolean constants

Convert them to shader booleans at earlier stage.

Signed-off-by: Axel Davy <axel.davy@ens.fr>
st/nine: Convert integer constants to floats before storing them when cards don't support integers

The shader code is already behaving as if they are floats when the the card doesn't support integers

Signed-off-by: Axel Davy <axel.davy@ens.fr>
st/nine: Use integers for loops when available

Signed-off-by: Axel Davy <axel.davy@ens.fr>