powerpc: rename ppc_pci_*_flags to pci_*_flags

This renames pci flags functions and enums in preparation for creating
generic version in asm-generic/pci-bridge.h. The following search and
replace is done:

s/ppc_pci_/pci_/
s/PPC_PCI_/PCI_/

Direct accesses to ppc_pci_flag variable are replaced with helper
functions.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>