powerpc/64: Move pci_device_from_OF_node() out of asm/pci-bridge.h

Move pci_device_from_OF_node() in pci64.c because it needs definition
of struct device_node and is not worth inlining.

ppc32.c already has it in pci32.c.

That way pci-bridge.h doesn't need linux/of.h (Brought by asm/prom.h
via asm/pci.h)

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/3c88286b55413730d7784133993a46ef4a3607ce.1646767214.git.christophe.leroy@csgroup.eu