Prefer BLENDVPD over VBLENDVPD if the latter doesn't save any
instructions.
VBLENDVPD allows separate source and destination registers, which can
eliminate a MOVAPD/MOVSD. However, on Intel since Skylake, VBLENDVPD
takes additional uops to execute compared to BLENDVPD (according to
https://uops.info). On AMD and older Intel microarchitectures there is no
difference.