target/arm: Convert "single-precision" register moves to decodetree

Convert the "single-precision" register moves to decodetree:
 * VMSR
 * VMRS
 * VMOV between general purpose register and single precision

Note that the VMSR/VMRS conversions make our handling of
the "should this UNDEF?" checks consistent between the two
instructions:
 * VMSR to MVFR0, MVFR1, MVFR2 now UNDEF from EL0
   (previously was a nop)
 * VMSR to FPSID now UNDEFs from EL0 or if VFPv3 or better
   (previously was a nop)
 * VMSR to FPINST and FPINST2 now UNDEF if VFPv3 or better
   (previously would write to the register, which had no
   guest-visible effect because we always UNDEF reads)

We also tighten up the decode: we were previously underdecoding
some SBZ or SBO bits.

The conversion of VMOV_single includes the expansion out of the
gen_mov_F0_vreg()/gen_vfp_mrs() and gen_mov_vreg_F0()/gen_vfp_msr()
sequences into the simpler direct load/store of the TCG temp via
neon_{load,store}_reg32(): we know in the new function that we're
always single-precision, we don't need to use the old-and-deprecated
cpu_F0* TCG globals, and we don't happen to have the declaration of
gen_vfp_msr() and gen_vfp_mrs() at the point in the file where the
new function is.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

target/arm/vfp.decode

@@ -62,3 +62,7 @@ VMOV_from_gp ---- 1110 0 0 index:1 0 .... rt:4 1011 .00 1 0000 \
 
 VDUP         ---- 1110 1 b:1 q:1 0 .... rt:4 1011 . 0 e:1 1 0000 \
              vn=%vn_dp
+
+VMSR_VMRS    ---- 1110 111 l:1 reg:4 rt:4 1010 0001 0000
+VMOV_single  ---- 1110 000 l:1 .... rt:4 1010 . 001 0000 \
+             vn=%vn_sp