target/i386: fix operand size for VCOMI/VUCOMI instructions

target/i386: fix operand size for VCOMI/VUCOMI instructions

Compared to other SSE instructions, VUCOMISx and VCOMISx are different:
the single and double precision versions are distinguished through a
prefix, however they use no-prefix and 0x66 for SS and SD respectively.
Scalar values usually are associated with 0xF2 and 0xF3.

Because of these, they incorrectly perform a 128-bit memory load instead
of a 32- or 64-bit load.  Fix this by writing a custom decoding function.

I tested that the reproducer is fixed and the test-avx output does not
change.

Reported-by: Gabriele Svelto <gsvelto@mozilla.com>
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1637
Fixes: f8d19eec0d53 ("target/i386: reimplement 0x0f 0x28-0x2f, add AVX", 2022-10-18)
Cc: qemu-stable@nongnu.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>