Provide a generic LRU walker in TTM, in the spirit of drm_gem_lru_scan()
but building on the restartable TTM LRU functionality.

The LRU walker optionally supports locking objects as part of
a ww mutex locking transaction, to mimic to some extent the
current functionality in ttm. However any -EDEADLK return
is converted to -ENOSPC and then to -ENOMEM before reaching
the driver, so that the driver will need to backoff and possibly retry
without being able to keep the ticket.

v3:
- Move the helper to core ttm.
- Remove the drm_exec usage from it for now, it will be
  reintroduced later in the series.
v4:
- Handle the -EALREADY case if ticketlocking.
v6:
- Some cleanup and added code comments (Matthew Brost)
- Clarified the ticketlock in the commit message (Matthew Brost)
v7:
- Use s64 rather than long for the target and progress
  (Christian König)
- Update documentation to not encourage using pages as a
  progress measure. (Christian König)
- Remove cond_resched(). (Christian König)

Cc: Christian König <christian.koenig@amd.com>
Cc: Somalapuram Amaranath <Amaranath.Somalapuram@amd.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: <dri-devel@lists.freedesktop.org>
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com> #v6
Link: https://patchwork.freedesktop.org/patch/msgid/20240705153206.68526-6-thomas.hellstrom@linux.intel.comSigned-off-by: Christian König <christian.koenig@amd.com>