env: Implement support for encrypting environment

Add function which allows encrypting the whole environment block with
AES-128-CBC. The key for the environment is retrieved by
env_aes_cbc_get_key() function, which must be implemented on a per-board
basis.

Signed-off-by: Marek Vasut <marex@denx.de>
diff --git a/include/environment.h b/include/environment.h
index f797595..08679aea 100644
--- a/include/environment.h
+++ b/include/environment.h
@@ -146,7 +146,12 @@
 extern char *env_name_spec;
 #endif
 
+#ifdef CONFIG_ENV_AES
+/* Make sure the payload is multiple of AES block size */
+#define ENV_SIZE ((CONFIG_ENV_SIZE - ENV_HEADER_SIZE) & ~(16 - 1))
+#else
 #define ENV_SIZE (CONFIG_ENV_SIZE - ENV_HEADER_SIZE)
+#endif
 
 typedef struct environment_s {
 	uint32_t	crc;		/* CRC32 over data bytes	*/
@@ -154,7 +159,12 @@
 	unsigned char	flags;		/* active/obsolete flags	*/
 #endif
 	unsigned char	data[ENV_SIZE]; /* Environment data		*/
-} env_t;
+} env_t
+#ifdef CONFIG_ENV_AES
+/* Make sure the env is aligned to block size. */
+__attribute__((aligned(16)))
+#endif
+;
 
 #ifdef ENV_IS_EMBEDDED
 extern env_t environment;