PCI: mvebu: Remove ARCH_KIRKWOOD dependency

mach-kirkwood has been removed, now that kirkwood lives in mach-mvebu.
ARCH_MVEBU is sufficient.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Jason Cooper <jason@lakedaemon.net>