Keystore 2.0: Implement convertStorageKeyToEphemeral() for km_compat

Implement the convertStorageKeyToEphemeral() function introduced into
IKeymintDevice for vold to get ephemeral per-boot keys from wrapped
storage keys.

Bug: 181806377
Bug: 181910578
Change-Id: Ib203edb529d0e0dbd6368ce62be20538a37d20b6
2 files changed