ARM: pci: make pcibios_assign_all_busses use pci_has_flag

Convert pcibios_assign_all_busses from a define to inline so platforms can
control this setting.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>