Use SHA256 for 32 byte keys

For NIAP certification keys need to be generated using SHA256 or
higher. Presently SHA1 is used. To satisfy this requirement,
SHA256 will be used for new keys. As the master key has recently
increased in size, the key size is used to determine if SHA1 is used
(for older keys) or SHA256.

Bug: 121272336
Test: Ran Keystore CTS tests against Walleye,
      no new test failures observed
Change-Id: Ic5f7840e60817d02b62dca7221f5cc703558db44
Merged-In: I6099156173e04b22c6edafd9fb0e072f7201c5ee