target/ppc: Add extra float instructions to POWER5P processors

ISA v2.03 introduced Floating Round to Integer instructions : frin,
friz, frip, and frim. Add them to POWER5+.

The PPC_FLOAT_EXT flag also includes the fre (Floating Reciprocal
Estimate) instruction which was introduced in ISA v2.0x. The
architecture document says its optional and that might be the reason
why it has been kept under the PPC_FLOAT_EXT flag. This means 970 CPUs
can not use it under QEMU, which doesn't seem to be a problem.

Signed-off-by: Cédric Le Goater <clg@kaod.org>