char: tpm: cr50: Move i2c locking to request/relinquish locality ops

Move i2c locking primitives to request_locality and relinquish_locality
callbacks, what effectively blocks TPM bus for the whole duration of
logical TPM operation.

With this in place, cr50-equipped TPM may be shared with external CPUs -
assuming that underneath i2c controller driver is aware of this setup
(see i2c-designware-amdpsp as an example).

Signed-off-by: Jan Dabros <jsd@semihalf.com>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>