MIPS: cavium-octeon: fix early boot hang on EBH5600 board

The boot hangs early on EBH5600 board when octeon_fdt_pip_iface() is
trying enumerate a non-existant interface. The actual hang happens in
cvmx_helper_interface_get_mode():

	mode.u64 = cvmx_read_csr(CVMX_GMXX_INF_MODE(interface));

when interface == 4. We can avoid this situation by first checking that
the interface exists in the DTB.

Signed-off-by: Aaro Koskinen <aaro.koskinen@nsn.com>
Acked-by: David Daney <david.daney@cavium.com>
Signed-off-by: John Crispin <blogic@openwrt.org>
Patchwork: http://patchwork.linux-mips.org/patch/6101/

arch/mips/cavium-octeon/octeon-platform.c

@@ -336,14 +336,14 @@ static void __init octeon_fdt_pip_iface(int pip, int idx, u64 *pmac)
 	int p;
 	int count = 0;
 
-	if (cvmx_helper_interface_enumerate(idx) == 0)
-		count = cvmx_helper_ports_on_interface(idx);
-
 	snprintf(name_buffer, sizeof(name_buffer), "interface@%d", idx);
 	iface = fdt_subnode_offset(initial_boot_params, pip, name_buffer);
 	if (iface < 0)
 		return;
 
+	if (cvmx_helper_interface_enumerate(idx) == 0)
+		count = cvmx_helper_ports_on_interface(idx);
+
 	for (p = 0; p < 16; p++)
 		octeon_fdt_pip_port(iface, idx, p, count - 1, pmac);
 }