Add auth token parsing to IKeymasterDevice.hal

Auth tokens have an unfortunate dual character. To most of the system
they are opaque blobs that are intended only to be obtained from one
HAL (e.g. gatekeeper or fingerprint) and passed to another
HAL (keymaster), but keystore actually needs to extract some bits of
information from them in order to determine which of the available blobs
should be provided for a given keymaster key operation.

This CL adds a method that resolves this dual nature by moving the
responsibility of parsing blobs to the HAL so that no component of the
framework has to make any assumptions about their content and all can
treat them as fully opaque. This still means that the various HAL
implementers have to agree on content, but they also have to agree on an
HMAC key which much be securely distributed to all at every boot, so
asking them to agree on an auth token format is perfectly
acceptable. But now the Android system doesn't have to care about the
format.

Bug: 32962548
Test: CTS tests pass, plus manual testing.
Change-Id: I78aa6e4ea9c5d8f34906b0969909387e2c5894e6