Change the bitwise encoding of key type categories

There were only 5 categories (now 4). Reduce the category mask from 7
bits to 3.

Combine unformatted, not-necessarily-uniform keys (HMAC, derivation)
with raw data.

Reintroduce a KEY_TYPE_IS_UNSTRUCTURED macro (which used to exist
under the name KEY_TYPE_IS_RAW_DATA macro) for key types that don't
have any structure, including both should-be-uniform keys (such as
block cipher and stream cipher keys) and not-necessarily-uniform
keys (such as HMAC keys and secrets for key derivation).

library/psa_crypto.c

@@ -135,9 +135,7 @@ typedef struct
 
 static int key_type_is_raw_bytes( psa_key_type_t type )
 {
-    psa_key_type_t category = type & PSA_KEY_TYPE_CATEGORY_MASK;
-    return( category == PSA_KEY_TYPE_RAW_DATA ||
-            category == PSA_KEY_TYPE_CATEGORY_SYMMETRIC );
+    return( PSA_KEY_TYPE_IS_UNSTRUCTURED( type ) );
 }
 
 typedef struct