xen/arm: optee: add fast calls handling

xen/arm: optee: add fast calls handling

This patch adds handling for the fast SMCs. As name suggests, those
calls can't be preempted and are used for auxiliary tasks such as
information retrieval. Most handlers are quite trivial, with exception
for capabilities information.

Capabilities exchange should be filtered out, so only caps
known to mediator are used. Also mediator disables static SHM
memory capability, because it can't share OP-TEE memory with a domain.
Only domain can share memory with OP-TEE, so it ensures that OP-TEE
supports dynamic SHM.

Basically, static SHM is a reserved memory region which is always
mapped into OP-TEE address space. It belongs to OP-TEE. Normally,
NW is allowed to access there, so it can communicate with OP-TEE.

On other hand, dynamic SHM is NW's own memory, which it can share
with OP-TEE. OP-TEE maps this memory dynamically, when it wants to
access it.

Because mediator can't share one static SHM region with all guests, it
just disables it for all of them. It is possible to make exception for
Dom0, but it requires separate handling for buffers allocated from
that region. Thus, it is not implemented yet.

Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@epam.com>
Acked-by: Julien Gral <julien.grall@arm.com>