lavu/hmac: Add support for SHA-2

Includes HMAC-SHA-224, HMAC-SHA-256, HMAC-SHA-384, and HMAC-SHA-512.
Tested using test vectors from https://tools.ietf.org/html/rfc4231

Signed-off-by: James Almer <jamrial@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavutil/hmac.h

@@ -32,6 +32,10 @@
 enum AVHMACType {
     AV_HMAC_MD5,
     AV_HMAC_SHA1,
+    AV_HMAC_SHA224 = 10,
+    AV_HMAC_SHA256,
+    AV_HMAC_SHA384,
+    AV_HMAC_SHA512,
 };
 
 typedef struct AVHMAC AVHMAC;