tee: add tee_shm_alloc_dma_mem()

tee: add tee_shm_alloc_dma_mem()

Add tee_shm_alloc_dma_mem() to allocate DMA memory. The memory is
represented by a tee_shm object using the new flag TEE_SHM_DMA_MEM to
identify it as DMA memory. The allocated memory will later be lent to
the TEE to be used as protected memory.

Reviewed-by: Sumit Garg <sumit.garg@oss.qualcomm.com>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>