[Arm] Do not lower vmax/vmin to Neon instructions

On some Arm cores there is a performance penalty when forwarding from an
S register to a D register.  Calculating VMAX in a D register creates
false forwarding hazards, so don't do that unless we're on a core which
specifically asks for it.

Patch by James Greenhalgh

Differential Revision: https://reviews.llvm.org/D75248