drivers/of: include export.h for EXPORT_SYMBOL_GPL/THIS_MODULE as required

For files that were getting these macros via the implicit presence
of module.h being everywhere.

With contributions from Stephen Rothwell <sfr@canb.auug.org.au>.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

drivers/of/of_net.c

@@ -9,6 +9,7 @@
 #include <linux/kernel.h>
 #include <linux/of_net.h>
 #include <linux/phy.h>
+#include <linux/export.h>
 
 /**
  * It maps 'enum phy_interface_t' found in include/linux/phy.h