[POWERPC] Disable broken PPC_PTRACE_GETFPREGS on 32 bits

The handling of PPC_PTRACE_GETFPREGS is broken on 32 bits kernel,
it will only return half of the registers. Since that call didn't
initially exist for 32 bits kernel (added recently), rather than
fixing it, let's just remove it.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>