Add back mul/sqr to CurveGFp [ci skip]
Add back mul/sqr to CurveGFp [ci skip]

These were available in 2.4 and while users "shouldn't" be using
CurveGFp, it is an exposed API.

webmaster128/botan,webmaster128/botan,randombit/botan,webmaster128/botan,webmaster128/botan,randombit/botan,webmaster128/botan,randombit/botan,randombit/botan,randombit/botan