nitro_enclaves: Add ioctl interface definition

The Nitro Enclaves driver handles the enclave lifetime management. This
includes enclave creation, termination and setting up its resources such
as memory and CPU.

An enclave runs alongside the VM that spawned it. It is abstracted as a
process running in the VM that launched it. The process interacts with
the NE driver, that exposes an ioctl interface for creating an enclave
and setting up its resources.

Changelog

v9 -> v10

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

v8 -> v9

* No changes.

v7 -> v8

* Add NE custom error codes for user space memory regions not backed by
pages multiple of 2 MiB, invalid flags and enclave CID.
* Add max flag value for enclave image load info.

v6 -> v7

* Clarify in the ioctls documentation that the return value is -1 and
errno is set on failure.
* Update the error code value for NE_ERR_INVALID_MEM_REGION_SIZE as it
gets in user space as value 25 (ENOTTY) instead of 515. Update the
NE custom error codes values range to not be the same as the ones
defined in include/linux/errno.h, although these are not propagated
to user space.

v5 -> v6

* Fix typo in the description about the NE CPU pool.
* Update documentation to kernel-doc format.
* Remove the ioctl to query API version.

v4 -> v5

* Add more details about the ioctl calls usage e.g. error codes, file
descriptors used.
* Update the ioctl to set an enclave vCPU to not return a file
descriptor.
* Add specific NE error codes.

v3 -> v4

* Decouple NE ioctl interface from KVM API.
* Add NE API version and the corresponding ioctl call.
* Add enclave / image load flags options.

v2 -> v3

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

v1 -> v2

* Add ioctl for getting enclave image load metadata.
* Update NE_ENCLAVE_START ioctl name to NE_START_ENCLAVE.
* Add entry in Documentation/userspace-api/ioctl/ioctl-number.rst for NE
ioctls.
* Update NE ioctls definition based on the updated ioctl range for major
and minor.

Reviewed-by: Alexander Graf <graf@amazon.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Alexandru Vasile <lexnv@amazon.com>
Signed-off-by: Andra Paraschiv <andraprs@amazon.com>
Link: https://lore.kernel.org/r/20200921121732.44291-2-andraprs@amazon.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>