drm/doc/rfc: VM_BIND uapi definition

VM_BIND and related uapi definitions

v2: Reduce the scope to simple Mesa use case.
v3: Expand VM_UNBIND documentation and add
    I915_GEM_VM_BIND/UNBIND_FENCE_VALID
    and I915_GEM_VM_BIND_TLB_FLUSH flags.
v4: Remove I915_GEM_VM_BIND_TLB_FLUSH flag and add additional
    documentation for vm_bind/unbind.
v5: Remove TLB flush requirement on VM_UNBIND.
    Add version support to stage implementation.
v6: Define and use drm_i915_gem_timeline_fence structure for
    all timeline fences.
v7: Rename I915_PARAM_HAS_VM_BIND to I915_PARAM_VM_BIND_VERSION.
    Update documentation on async vm_bind/unbind and versioning.
    Remove redundant vm_bind/unbind FENCE_VALID flag, execbuf3
    batch_count field and I915_EXEC3_SECURE flag.
v8: Remove I915_GEM_VM_BIND_READONLY and minor documentation
    updates.

Signed-off-by: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220701003110.24843-4-niranjana.vishwanathapura@intel.com