PCI: rpaphp: Rename rpaphp_register_pci_slot() to rpaphp_enable_slot()

Rename rpaphp_register_pci_slot() because its easy to confuse
with  rpaphp_register_slot() even though it does something 
completely different. Rename it to rpaphp_enable_slot() because
its almost identical to enbale_slot().

Signed-off-by: Linas Vepstas <linas@austin.ibm.com>
Cc: John Rose <johnrose@austin.ibm.com>
Signed-off-by: Kristen Carlson Accardi <kristen.c.accardi@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>