lima/ppir: simplify select op lowering and scheduling

lima/ppir: simplify select op lowering and scheduling

The select operation relies on the select condition coming from the
result of the the alu scalar mult slot, in the same instruction.
The current implementation creates a mov node to be the predecessor of
select, and then relies on an exception during scheduling to ensure that
both ops are inserted in the same instruction.

Now that the ppir scheduler supports pipeline register dependencies,
this can be simplified by making the mov explicitly output to the fmul
pipeline register, and the scheduler can place it without an exception.

Since the select condition can only be placed in the scalar mult slot,
differently than a regular mov, define a separate op for it.

Signed-off-by: Erico Nunes <nunes.erico@gmail.com>
Reviewed-by: Vasily Khoruzhick <anarsoul@gmail.com>
Reviewed-by: Qiang Yu <yuq825@gmail.com>