program: Shrink and rename SaturateMode field to Saturate.

program: Shrink and rename SaturateMode field to Saturate.

It was 2 bits to accommodate SATURATE_PLUS_MINUS_ONE (removed by commit
09b566e1). A similar change was made to TGSI recently in commit
e1c4e8aa.

Reducing the size from 2 bits to 1 reduces the size of the bit fields
from 17 bits to 16, which is a much nicer number.

Reviewed-by: Brian Paul <brianp@vmware.com>