pci: move microblaze and powerpc pci flag functions into asm-generic

Move separate microblaze and powerpc pci flag functions pci_set_flags,
pci_add_flags, and pci_has_flag into asm-generic/pci-bridge.h so other
archs can use them.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Michal Simek <monstr@monstr.eu>