powerpc: Fix SMP issues with ppc64le ABIv2

There is no need to put a function descriptor in
__secondary_hold_spinloop. Use ppc_function_entry to get the
instruction address and put it in __secondary_hold_spinloop instead.

Also fix an issue where we assumed cur_cpu_spec held a function
descriptor.

Signed-off-by: Anton Blanchard <anton@samba.org>
powerpc: Fix ABIv2 issue with dereference_function_descriptor

Don't try and dereference a function descriptor on ABIv2.

Signed-off-by: Anton Blanchard <anton@samba.org>