gallivm: Do size computations simultanously for all dimensions (AoS).

gallivm: Do size computations simultanously for all dimensions (AoS).

Operate simultanouesly on <width, height, depth> vector as much as possible,
instead of doing the operations on vectors with broadcasted scalars.

Also do the 24.8 fixed point scalar with integer shift of the texture size,
for unnormalized coordinates.

AoS path only for now -- the same thing can be done for SoA.