[AMDGPU] Divergence driven selection for fused bitlogic

The change adds divergence predicates for fused logical operations.
The problem with selecting a scalar fused op such as S_NOR_B32 is
that it does not have a VALU counterpart and will be split in
moveToVALU. At the same time it prevents selection of a better
opcode on the VALU side (such as V_OR3_B32) which does not have a
counterpart on SALU side.

XNOR opcodes are left as is and selected as scalar to get advantage
of the SIInstrInfo::lowerScalarXnor() code which can commute
operations to keep one of two opcodes on SALU if possible. See
xnor.ll test for this.

Differential Revision: https://reviews.llvm.org/D111907