tile: export a handful of symbols appropriately

This was shown up by running with "allmodconfig".  I used
EXPORT_SYMBOL() to match existing conventions in files that
were already exporting symbols, or that were exported that way
by other architectures, and otherwise EXPORT_SYMBOL_GPL().

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>

arch/tile/kernel/reboot.c

@@ -16,6 +16,7 @@
 #include <linux/reboot.h>
 #include <linux/smp.h>
 #include <linux/pm.h>
+#include <linux/export.h>
 #include <asm/page.h>
 #include <asm/setup.h>
 #include <hv/hypervisor.h>
@@ -49,3 +50,4 @@ void machine_restart(char *cmd)
 
 /* No interesting distinction to be made here. */
 void (*pm_power_off)(void) = NULL;
+EXPORT_SYMBOL(pm_power_off);