Adding tuning flags for int <-> fp domain switching penalties; NFC

Atom
    - No domain switching penalties
Nehalem+
    - No penalty on moves
Haswell+
    - No penalty on moves / shuffles
Skylake+
    - No penality on moves / shuffles / blends

Reviewed By: RKSimon

Differential Revision: https://reviews.llvm.org/D143859