firmware: tee_bnxt: Release TEE shm, session, and context during kexec

Implement a .shutdown hook that will be called during a kexec operation
so that the TEE shared memory, session, and context that were set up
during .probe can be properly freed/closed.

Additionally, don't use dma-buf backed shared memory for the
fw_shm_pool. dma-buf backed shared memory cannot be reliably freed and
unregistered during a kexec operation even when tee_shm_free() is called
on the shm from a .shutdown hook. The problem occurs because
dma_buf_put() calls fput() which then uses task_work_add(), with the
TWA_RESUME parameter, to queue tee_shm_release() to be called before the
current task returns to user mode. However, the current task never
returns to user mode before the kexec completes so the memory is never
freed nor unregistered.

Use tee_shm_alloc_kernel_buf() to avoid dma-buf backed shared memory
allocation so that tee_shm_free() can directly call tee_shm_release().
This will ensure that the shm can be freed and unregistered during a
kexec operation.

Fixes: 246880958ac9 ("firmware: broadcom: add OP-TEE based BNXT f/w manager")
Cc: [email protected]
Signed-off-by: Allen Pais <[email protected]>
Co-developed-by: Tyler Hicks <[email protected]>
Signed-off-by: Tyler Hicks <[email protected]>
Reviewed-by: Sumit Garg <[email protected]>
Acked-by: Florian Fainelli <[email protected]>
Signed-off-by: Jens Wiklander <[email protected]>

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