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>
diff --git a/drivers/of/of_pci_irq.c b/drivers/of/of_pci_irq.c
index ac1ec54..9312516 100644
--- a/drivers/of/of_pci_irq.c
+++ b/drivers/of/of_pci_irq.c
@@ -1,6 +1,7 @@
 #include <linux/kernel.h>
 #include <linux/of_pci.h>
 #include <linux/of_irq.h>
+#include <linux/export.h>
 #include <asm/prom.h>
 
 /**