The `sad` instruction (used for iadd3) doesn't support the scalar ALU.
This means we might fall back to non-earlypreamble whenever we use it in
the preamble. Prevent this by emitting it as two adds instead.
Signed-off-by: Job Noorman <jnoorman@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/32943>