[enco] Support constant folding for add, sub, mul, div, sqrt (#2821)

[enco] Support constant folding for add, sub, mul, div, sqrt (#2821)

* [enco] Support constant folding for add, sub, mul, div, sqrt

Until now, only `coco::Copy` instruction was available for constant folding.
This commit will support some `coco::Eval` instructions in constant folding,
which is add, sub, mul, div, sqrt.

Signed-off-by: Seok NamKoong <sk.namkoong@samsung.com>
* minor modifications