ARM/keystone: move the DMA offset handling under ifdef CONFIG_ARM_LPAE

The DMA offset notifier can only be used if PHYS_OFFSET is at least
KEYSTONE_HIGH_PHYS_START, which can't be represented by a 32-bit
phys_addr_t.  Currently the code compiles fine despite that, a pending
change to the DMA offset handling would create a compiler warning for
this case.  Add an ifdef to not compile the code except for LPAE
configs.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>

arch/arm/mach-keystone/keystone.c

@@ -24,6 +24,7 @@
 
 #include "keystone.h"
 
+#ifdef CONFIG_ARM_LPAE
 static unsigned long keystone_dma_pfn_offset __read_mostly;
 
 static int keystone_platform_notifier(struct notifier_block *nb,
@@ -48,14 +49,17 @@ static int keystone_platform_notifier(struct notifier_block *nb,
 static struct notifier_block platform_nb = {
 	.notifier_call = keystone_platform_notifier,
 };
+#endif /* CONFIG_ARM_LPAE */
 
 static void __init keystone_init(void)
 {
+#ifdef CONFIG_ARM_LPAE
 	if (PHYS_OFFSET >= KEYSTONE_HIGH_PHYS_START) {
 		keystone_dma_pfn_offset = PFN_DOWN(KEYSTONE_HIGH_PHYS_START -
 						   KEYSTONE_LOW_PHYS_START);
 		bus_register_notifier(&platform_bus_type, &platform_nb);
 	}
+#endif
 	keystone_pm_runtime_init();
 }