drm: Add four ioctls for managing drm mode object leases [v7]

drm_mode_create_lease

	Creates a lease for a list of drm mode objects, returning an
	fd for the new drm_master and a 64-bit identifier for the lessee

drm_mode_list_lesees

	List the identifiers of the lessees for a master file

drm_mode_get_lease

	List the leased objects for a master file

drm_mode_revoke_lease

	Erase the set of objects managed by a lease.

This should suffice to at least create and query leases.

Changes for v2 as suggested by Daniel Vetter <daniel.vetter@ffwll.ch>:

 * query ioctls only query the master associated with
   the provided file.

 * 'mask_lease' value has been removed

 * change ioctl has been removed.

Changes for v3 suggested in part by Dave Airlie <airlied@gmail.com>

 * Add revoke ioctl.

Changes for v4 suggested by Dave Airlie <airlied@gmail.com>

 * Expand on the comment about the magic use of &drm_lease_idr_object
 * Pad lease ioctl structures to align on 64-bit boundaries

Changes for v5 suggested by Dave Airlie <airlied@gmail.com>

 * Check for non-negative object_id in create_lease to avoid debug
   output from the kernel.

Changes for v6 provided by Dave Airlie <airlied@gmail.com>

 * For non-universal planes add primary/cursor planes to lease

   If we aren't exposing universal planes to this userspace client,
   and it requests a lease on a crtc, we should implicitly export the
   primary and cursor planes for the crtc.

   If the lessee doesn't request universal planes, it will just see
   the crtc, but if it does request them it will then see the plane
   objects as well.

   This also moves the object look ups earlier as a side effect, so
   we'd exit the ioctl quicker for non-existant objects.

 * Restrict leases to crtc/connector/planes.

   This only allows leasing for objects we wish to allow.

Changes for v7 provided by Dave Airlie <airlied@gmail.com>

 * Check pad args are 0
 * Check create flags and object count are valid.
 * Check return from fd allocation
 * Refactor lease idr setup and add some simple validation
 * Use idr_mutex uniformly (Keith)

Signed-off-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>