pseries: Separate PCI RTAS setup from common from emulation specific PCI setup

pseries: Separate PCI RTAS setup from common from emulation specific PCI setup

Currently the RTAS functions for handling PCI are registered from the
class init code for the PCI host bridge.  That sort of makes sense
now, but will break in the future when vfio gives us multiple types of
host bridge for pseries (emulated and pass-through, at least).  The
RTAS functions will be common across all host bridge types (and will
call out to different places internally depending on the type).

So, this patch moves the RTAS registration into its own function
called direct from the machine setup code.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Alexander Graf <agraf@suse.de>