Increase the master key size to 256 bits

NIAP certification finds that the 128 bit key size is insufficient
and requires a 256 bit key size. This change increases the
size of new master keys to 256 bits. Any existing master keys are
not changed and continue to be supported.

A new BlobType, TYPE_MASTER_KEY_AES256, is used to signal when a
key is the new larger size.

Bug: 121272336
Test: (1) Ran Keystore CTS tests against Walleye.
      (2) Created keys in build without change, moved to build
          with change and verified old key could be loaded and
	  used. Also, a new key could be created with the
	  increased size and could be reloaded after a reboot.
Change-Id: If00331c303e6cc7bc95a2ab624d0e19bec4e587e
diff --git a/keystore/blob.h b/keystore/blob.h
index 8d68fc4..77b6f38 100644
--- a/keystore/blob.h
+++ b/keystore/blob.h
@@ -36,6 +36,7 @@
 constexpr size_t kAesKeySize = 128 / 8;
 constexpr size_t kGcmTagLength = 128 / 8;
 constexpr size_t kGcmIvLength = 96 / 8;
+constexpr size_t kAes128KeySizeBytes = 128 / 8;
 
 /* Here is the file format. There are two parts in blob.value, the secret and
  * the description. The secret is stored in ciphertext, and its original size
@@ -88,6 +89,7 @@
     TYPE_KEYMASTER_10 = 4,
     TYPE_KEY_CHARACTERISTICS = 5,
     TYPE_KEY_CHARACTERISTICS_CACHE = 6,
+    TYPE_MASTER_KEY_AES256 = 7,
 } BlobType;
 
 class LockedKeyBlobEntry;