lima/ppir: add fallback mov option for const scheduler

lima/ppir: add fallback mov option for const scheduler

It turns out that with more aggressive combining, there can be cases
where the available const slots are not enough for one instruction.
In particular, fcsel can take up to two consts, and a previous alu slot,
such as a comparison condition, might require an additional const.
So add a fallback for it like for uniforms.

Signed-off-by: Erico Nunes <nunes.erico@gmail.com>
Reviewed-by: Vasily Khoruzhick <anarsoul@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4632>