ide: add configuration

CONFIG_IDE_SWAP_IO

This configuration option replaces a complex conditional
in cmd_ide.c with an explicit define to be added to SoC or
board configs.

Signed-off-by: Albert Aribaud <albert.aribaud@free.fr>
diff --git a/arch/powerpc/include/asm/config.h b/arch/powerpc/include/asm/config.h
index f70699d..d098657 100644
--- a/arch/powerpc/include/asm/config.h
+++ b/arch/powerpc/include/asm/config.h
@@ -95,4 +95,7 @@
 #define CONFIG_FSL_LBC
 #endif
 
+/* All PPC boards must swap IDE bytes */
+#define CONFIG_IDE_SWAP_IO
+
 #endif /* _ASM_CONFIG_H_ */