at91: corvus_defconfig: get rid of build warnings

fix CONFIG_OF_EMBED and add CONFIG_DM_USB
build warnings.

Signed-off-by: Heiko Schocher <hs@denx.de>
diff --git a/include/configs/corvus.h b/include/configs/corvus.h
index 749a67d..e85f684 100644
--- a/include/configs/corvus.h
+++ b/include/configs/corvus.h
@@ -72,6 +72,7 @@
 #define CONFIG_SYS_NAND_MASK_CLE		(1 << 22)
 #define CONFIG_SYS_NAND_ENABLE_PIN		AT91_PIN_PC14
 #define CONFIG_SYS_NAND_READY_PIN		AT91_PIN_PC8
+#define CONFIG_SYS_NAND_DRIVER_ECC_LAYOUT
 #endif
 
 /* Ethernet */