include/linux/of.h: provide of_n_{addr,size}_cells wrappers for !CONFIG_OF

The pci-rcar driver is enabled for compile tests, and this has shown that
the driver cannot build without CONFIG_OF, following the inclusion of
commit f8f2fe73 ("PCI: rcar: Use new OF interrupt mapping when possible"):

  drivers/pci/host/pcie-rcar.c: In function 'pci_dma_range_parser_init':
  drivers/pci/host/pcie-rcar.c:1039:2: error: implicit declaration of function 'of_n_addr_cells' [-Werror=implicit-function-declaration]
    parser->pna = of_n_addr_cells(node);
    ^

As pointed out by Ben Dooks and Geert Uytterhoeven, this is actually
supposed to build fine, which we can achieve if we make the declaration
of of_irq_parse_and_map_pci conditional on CONFIG_OF and provide an
empty inline function otherwise, as we do for a lot of other of
interfaces.

This lets us build the rcar_pci driver again without CONFIG_OF for build
testing.  All platforms using this driver select OF, so this doesn't
change anything for the users.

[akpm@linux-foundation.org: be consistent with surrounding code]
Link: http://lkml.kernel.org/r/20170911200805.3363318-1-arnd@arndb.de
Fixes: c25da477 ("PCI: rcar: Add Renesas R-Car PCIe driver")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Frank Rowand <frank.rowand@sony.com>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Magnus Damm <damm@opensource.se>
Cc: Ben Dooks <ben.dooks@codethink.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/of.h

@@ -734,6 +734,16 @@ static inline struct device_node *of_get_cpu_node(int cpu,
 	return NULL;
 }
 
+static inline int of_n_addr_cells(struct device_node *np)
+{
+	return 0;
+
+}
+static inline int of_n_size_cells(struct device_node *np)
+{
+	return 0;
+}
+
 static inline int of_property_read_u64(const struct device_node *np,
 				       const char *propname, u64 *out_value)
 {