dma-buf: Add constraints sharing information

At present, struct device lacks a mechanism of exposing memory
access constraints for the device.

Consequently, there is also no mechanism to share these constraints
while sharing buffers using dma-buf.

If we add support for sharing such constraints, we could use that
to try to collect requirements of different buffer-sharing devices
to allocate buffers from a pool that satisfies requirements of all
such devices.

This is an attempt to add this support; at the moment, only a bitmask
is added, but if post discussion, we realise we need more information,
we could always extend the definition of constraint.

A new dma-buf op is also added, to allow exporters to interpret or decide
on constraint-masks on their own. A default implementation is provided to
just AND (&) all the constraint-masks.

What constitutes a constraint-mask could be left for interpretation on a
per-platform basis, while defining some common masks.

Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
Cc: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-media@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Cc: linaro-mm-sig@lists.linaro.org

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