tee: make tee_shm_register_kernel_buf vmalloc supported

In some low-memory devices, it's hard to aquire large-orders pages,
this patch allowed user using scatter pages to register shm.

Signed-off-by: Phil Chang <phil.chang@mediatek.com>
Reviewed-by: Sumit Garg <sumit.garg@linaro.org>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>