mincrypt: support SHA-256 hash algorithm

- adds a library to compute the SHA-256 hash

- updates the RSA verifier to take an argument specifying either SHA-1
  or SHA-256

- updates DumpPublicKey to with new "key" version numbers for
  specifying SHA-256

- adds new argument to adb auth code to maintain existing behavior

(cherry picked from commit 515e1639)

Change-Id: Ib35643b3d864742e817ac6e725499b451e45afcf