ppc: Fix xsmaddmdp and friends

ppc: Fix xsmaddmdp and friends

A class of instructions of the form:
  op Target,A,B
which operate like:
  Target = Target * A + B
have a bit set which distinguishes them from instructions that operate as:
  Target = Target * B + A

This bit is not being checked properly (using PPC_BIT macro), so all
instructions in this class are operating incorrectly as the second form
above.  The bit was being checked as if it were part of a 64-bit
instruction opcode, rather than a proper 32-bit opcode.  Fix by using the
macro (PPC_BIT32) which treats the opcode as a 32-bit quantity.

Fixes: c9f4e4d8b632 ("target/ppc: improve VSX_FMADD with new GEN_VSX_HELPER_VSX_MADD macro")

Signed-off-by: Paul A. Clarke <pc@us.ibm.com>
Message-Id: <1566401321-22419-1-git-send-email-pc@us.ibm.com>
Reviewed-by: Laurent Vivier <lvivier@redhat.com>
Tested-by: Laurent Vivier <lvivier@redhat.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>