target-ppc: add maddhd and maddhdu instruction

target-ppc: add maddhd and maddhdu instruction

maddhd: Multiply-Add High Doubleword
maddhdu: Multiply-Add High Doubleword Unsigned

Above two instruction are dual form and differ by 1 bit
(31st bit)

Multiplies two 64-bit registers (RA * RB), adds third register(RC) to
the result(quadword) and returns the higher dword in the target
register(RT).

Signed-off-by: Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>