freedreno/ir3: handle imad24_ir3 case in UBO lowering

freedreno/ir3: handle imad24_ir3 case in UBO lowering

Similiar to iadd, we can fold an added constant value from an imad24_ir3
into the load_uniform's constant offset.  This avoids some cases where
the addition of imad24_ir3 could otherwise be a regression in instr
count.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Kristian H. Kristensen <hoegsberg@google.com>
Reviewed-by: Eduardo Lima Mitev <elima@igalia.com>