powerpc: add export.h to files making use of EXPORT_SYMBOL

With module.h being implicitly everywhere via device.h, the absence
of explicitly including something for EXPORT_SYMBOL went unnoticed.
Since we are heading to fix things up and clean module.h from the
device.h file, we need to explicitly include these files now.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
diff --git a/arch/powerpc/sysdev/mpc5xxx_clocks.c b/arch/powerpc/sysdev/mpc5xxx_clocks.c
index 34e12f9..96f815a 100644
--- a/arch/powerpc/sysdev/mpc5xxx_clocks.c
+++ b/arch/powerpc/sysdev/mpc5xxx_clocks.c
@@ -8,6 +8,7 @@
 
 #include <linux/kernel.h>
 #include <linux/of_platform.h>
+#include <linux/export.h>
 
 unsigned int
 mpc5xxx_get_bus_frequency(struct device_node *node)