arm: atmel: add nand trimffs subcommand for at91sam9n12 and at91sam9x5

as the at91sam9n12 and at91sam9x5 soc support PMECC, when use u-boot
to flash the rootfs, in order to avoid flash one sector with all 0xff
into NAND, so use nand trimffs subcommand to avoid it

Signed-off-by: Bo Shen <voice.shen@atmel.com>
Signed-off-by: Andreas Bießmann <andreas.devel@googlemail.com>

include/configs/at91sam9n12ek.h

@@ -122,6 +122,9 @@
 #define CONFIG_PMECC_CAP		2
 #define CONFIG_PMECC_SECTOR_SIZE	512
 #define CONFIG_PMECC_INDEX_TABLE_OFFSET	0x8000
+
+#define CONFIG_CMD_NAND_TRIMFFS
+
 #endif
 
 #define CONFIG_MTD_PARTITIONS

include/configs/at91sam9x5ek.h

@@ -123,6 +123,8 @@
 #define CONFIG_PMECC_SECTOR_SIZE	512
 #define CONFIG_PMECC_INDEX_TABLE_OFFSET	0x8000
 
+#define CONFIG_CMD_NAND_TRIMFFS
+
 #define CONFIG_MTD_DEVICE
 #define CONFIG_CMD_MTDPARTS
 #define CONFIG_MTD_PARTITIONS