aes: add a define for the size of a block

In the code, we use the size of the key for the
size of the block. It's true when the key is 128 bits,
but it become false for key of 192 bits and 256 bits.
So to prepare the support of aes192  and 256,
we introduce a constant for the iaes block size.

Signed-off-by: Philippe Reynes <philippe.reynes@softathome.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/include/uboot_aes.h b/include/uboot_aes.h
index 2fda384..1ae3ac9 100644
--- a/include/uboot_aes.h
+++ b/include/uboot_aes.h
@@ -18,7 +18,7 @@
  * AES encryption library, with small code size, supporting only 128-bit AES
  *
  * AES is a stream cipher which works a block at a time, with each block
- * in this case being AES_KEY_LENGTH bytes.
+ * in this case being AES_BLOCK_LENGTH bytes.
  */
 
 enum {
@@ -28,6 +28,7 @@
 
 	AES_KEY_LENGTH	= 128 / 8,
 	AES_EXPAND_KEY_LENGTH	= 4 * AES_STATECOLS * (AES_ROUNDS + 1),
+	AES_BLOCK_LENGTH	= 128 / 8,
 };
 
 /**
@@ -62,7 +63,7 @@
 /**
  * Apply chain data to the destination using EOR
  *
- * Each array is of length AES_KEY_LENGTH.
+ * Each array is of length AES_BLOCK_LENGTH.
  *
  * @cbc_chain_data	Chain data
  * @src			Source data