lima/ppir: optimizations in regalloc spilling code

lima/ppir: optimizations in regalloc spilling code

Avoid creating unnecessary instructions for the load/store temp nodes
when not required, to further reduce register pressure.

The store_temp operation seems to be unable to do any spilling.
At least the offline shader seems to never output instructions accessing
swizzled components, and attempting to output that in ppir results in
errors. So, force spilled registers to allocate a full vec4 register.
This seems to be the optimal way as it is possible to always keep stores
and temps in a single instruction that can be pipelined.

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