tpm2: add tpm2_get_name()

tpm2: add tpm2_get_name()

This adds functions to get the "name" of a key. The key "name", as defined
by the TPM2 spec, includes its entire public area (with attribute fields),
not only its key fingerprint.

A function is added to calculate the name of a provided key public area,
as well as a function to get the name of a key which is present in the TPM.