tee: implement protected DMA-heap

Implement DMA heap for protected DMA-buf allocation in the TEE
subsystem.

Protected memory refers to memory buffers behind a hardware enforced
firewall. It is not accessible to the kernel during normal circumstances
but rather only accessible to certain hardware IPs or CPUs executing in
higher or differently privileged mode than the kernel itself. This
interface allows to allocate and manage such protected memory buffers
via interaction with a TEE implementation.

The protected memory is allocated for a specific use-case, like Secure
Video Playback, Trusted UI, or Secure Video Recording where certain
hardware devices can access the memory.

The DMA-heaps are enabled explicitly by the TEE backend driver. The TEE
backend drivers needs to implement protected memory pool to manage the
protected memory.

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

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