Fix mainboard level enable_dev()

Commit 188e3c2ff0 dropped mainboard
out of the static device tree. This left dev_root->chip_ops unset,
and mainboard_ops.enable_dev() was no longer called.

Change-Id: I6d447c8049a66041b8bb36ec9aac3e7e0d20a99b
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/1374
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/include/device/device.h

@@ -165,6 +165,7 @@ void show_all_devs_resources(int debug_level, const char* msg);
 #define DEVICE_MEM_ALIGN 4096
 
 extern struct device_operations default_dev_ops_root;
+extern struct chip_operations mainboard_ops;
 void pci_domain_read_resources(struct device *dev);
 unsigned int pci_domain_scan_bus(struct device *dev, unsigned int max);
 unsigned int scan_static_bus(device_t bus, unsigned int max);