KEYS: trusted: tee: Refactor register SHM usage

The OP-TEE driver using the old SMC based ABI permits overlapping shared
buffers, but with the new FF-A based ABI each physical page may only
be registered once.

As the key and blob buffer are allocated adjancently, there is no need
for redundant register shared memory invocation. Also, it is incompatibile
with FF-A based ABI limitation. So refactor register shared memory
implementation to use only single invocation to register both key and blob
buffers.

[jarkko: Added cc to stable.]
Cc: stable@vger.kernel.org # v5.16+
Fixes: 4615e5a3

 ("optee: add FF-A support")
Reported-by: Jens Wiklander <jens.wiklander@linaro.org>
Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
Tested-by: Jens Wiklander <jens.wiklander@linaro.org>
Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>