optee: fix tee out of memory failure seen during kexec reboot

The following out of memory errors are seen on kexec reboot
from the optee core.

[    0.368428] tee_bnxt_fw optee-clnt0: tee_shm_alloc failed
[    0.368461] tee_bnxt_fw: probe of optee-clnt0 failed with error -22

tee_shm_release() is not invoked on dma shm buffer.

Implement .shutdown() method to handle the release of the buffers
correctly.

More info:
https://github.com/OP-TEE/optee_os/issues/3637



Cc: stable@vger.kernel.org
Signed-off-by: Allen Pais <apais@linux.microsoft.com>
Reviewed-by: Tyler Hicks <tyhicks@linux.microsoft.com>
Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>
Reviewed-by: Sumit Garg <sumit.garg@linaro.org>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>