[ARM] Only produce qadd8b under hasV6Ops
When compiling for a arm5te cpu from clang, the +dsp attribute is
set. This meant we could try and generate qadd8 instructions where we
would end up having no pattern. I've changed the condition here to be
hasV6Ops && hasDSP, which is what other parts of ARMISelLowering seem
to use for similar instructions.
Fixed PR45677.
This fixes "fatal error: error in backend: Cannot select: t37: i32 =
ARMISD::QADD8b t43, t44" when compiling sys/dev/sound/pcm/feeder_mixer.c
for armv5. For some reason we do not encounter this on head, but this
error popped up while building universes for stable/12.
MFC after: 3 days
702995b2a5