Lower some instructions, without much guarantee of
correctness. *Running* generated code will be risky
because the register allocator isn't aware of register
aliasing.

Fill in v{add,div,mul,sub}.f{32,64}, vmov, vldr
and vsqrt.f{32,64}. I tried to make the nacl-other-intrinsics
test not explode, so added vsqrt too. That was pretty
easy for sqrt, but then fabs tests also exploded. Those are not
truly fixed but are currently "fixed" by adding a FakeDef to
satisfy liveness.

Propagate float/double arguments to the right register
in lowerArguments, lowerCall, and propagate to s0/d0/q0
for lowerReturn. May need to double check the calling convention.
Currently can't test call-ret because vpush/vpop for prologues
and epilogues isn't done.

Legalize FP immediates to make the nacl-other-intrinsics sqrt
test happy. Use the correct type of load (vldr (.32 and .64 are
optional) instead of ldr{b,h,,d}).

Whether or not the float/vector instructions can be
predicated is a bit interesting. The float/double ones
can, but the SIMD versions cannot. E.g.

vadd<cond>.f32 s0, s0, s1 is okay
vadd<cond>.f32 q0, q0, q1 is not okay.

For now, just omit conditions from instructions that may
end up being reused for SIMD.

Split up the fp.pnacl.ll test into multiple ones so that
parts of lowering can be tested incrementally.

BUG= https://code.google.com/p/nativeclient/issues/detail?id=4076
R=stichnot@chromium.org

Review URL: https://codereview.chromium.org/1266263003 .