powerpc: Fix a build problem on ppc32 with new DMA_ATTRs

The new dma_attrs support must only be enabled for 64 bits as it's not
been implemented for 32 bits yet.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 5e21854..06b7277 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -113,7 +113,7 @@
 	select HAVE_KPROBES
 	select HAVE_KRETPROBES
 	select HAVE_LMB
-	select HAVE_DMA_ATTRS
+	select HAVE_DMA_ATTRS if PPC64
 
 config EARLY_PRINTK
 	bool