nitro_enclaves: Define the PCI device interface

nitro_enclaves: Define the PCI device interface

The Nitro Enclaves (NE) driver communicates with a new PCI device, that
is exposed to a virtual machine (VM) and handles commands meant for
handling enclaves lifetime e.g. creation, termination, setting memory
regions. The communication with the PCI device is handled using a MMIO
space and MSI-X interrupts.

This device communicates with the hypervisor on the host, where the VM
that spawned the enclave itself runs, e.g. to launch a VM that is used
for the enclave.

Define the MMIO space of the NE PCI device, the commands that are
provided by this device. Add an internal data structure used as private
data for the PCI device driver and the function for the PCI device
command requests handling.

Changelog

v9 -> v10

* Update commit message to include the changelog before the SoB tag(s).

v8 -> v9

* Fix indent for the NE PCI device command types enum.

v7 -> v8

* No changes.

v6 -> v7

* Update the documentation to include references to the NE PCI device id
  and MMIO bar.

v5 -> v6

* Update documentation to kernel-doc format.

v4 -> v5

* Add a TODO for including flags in the request to the NE PCI device to
  set a memory region for an enclave. It is not used for now.

v3 -> v4

* Remove the "packed" attribute and include padding in the NE data
  structures.

v2 -> v3

* Remove the GPL additional wording as SPDX-License-Identifier is
  already in place.

v1 -> v2

* Update path naming to drivers/virt/nitro_enclaves.
* Update NE_ENABLE_OFF / NE_ENABLE_ON defines.

Reviewed-by: Alexander Graf <graf@amazon.com>
Signed-off-by: Alexandru-Catalin Vasile <lexnv@amazon.com>
Signed-off-by: Alexandru Ciobotaru <alcioa@amazon.com>
Signed-off-by: Andra Paraschiv <andraprs@amazon.com>
Link: https://lore.kernel.org/r/20200921121732.44291-3-andraprs@amazon.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>