tcg-sparc: Implement division properly.

The {div,divu}2 opcodes are intended for systems for which the
division instruction produces both quotient and remainder.  Sparc
is not such a system.  Indeed, the remainder must be computed as

  quot = a / b
  rem = a - (quot * b)

Split out a tcg_out_div32 function that properly initializes Y
with the extension of the input to 64-bits.  Discard the code
that used the 64-bit DIVX on sparc9/sparcv8plus without extending
the inputs to 64-bits.  Implement remainders in terms of division
followed by multiplication.

Signed-off-by: Richard Henderson <rth@twiddle.net>
[blauwirbel@gmail.com: applied rth's typo fix in tcg_out_div32]
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
