KEYS: trusted: Add generic trusted keys framework

Current trusted keys framework is tightly coupled to use TPM device as
an underlying implementation which makes it difficult for implementations
like Trusted Execution Environment (TEE) etc. to provide trusted keys
support in case platform doesn't posses a TPM device.

Add a generic trusted keys framework where underlying implementations
can be easily plugged in. Create struct trusted_key_ops to achieve this,
which contains necessary functions of a backend.

Also, define a module parameter in order to select a particular trust
source in case a platform support multiple trust sources. In case its
not specified then implementation itetrates through trust sources list
starting with TPM and assign the first trust source as a backend which
has initiazed successfully during iteration.

Note that current implementation only supports a single trust source at
runtime which is either selectable at compile time or during boot via
aforementioned module parameter.

Suggested-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>

KEYS: trusted: Move TPM2 trusted keys code

Move TPM2 trusted keys code to trusted keys subsystem. The reason
being it's better to consolidate all the trusted keys code to a single
location so that it can be maintained sanely.

Also, utilize existing tpm_send() exported API which wraps the internal
tpm_transmit_cmd() API.

Suggested-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Tested-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>

KEYS: trusted: Create trusted keys subsystem

Move existing code to trusted keys subsystem. Also, rename files with
"tpm" as suffix which provides the underlying implementation.

Suggested-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Tested-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>