Uses the new simplified tee_shm_alloc_kernel_buf() function instead of
the old deprecated tee_shm_alloc() function which required specific
TEE_SHM-flags.
Reviewed-by: NSumit Garg <sumit.garg@linaro.org>
Signed-off-by: NJens Wiklander <jens.wiklander@linaro.org>