drm/vmwgfx: Assign eviction priorities to resources

TTM provides a means to assign eviction priorities to buffer object. This
means that all buffer objects with a lower priority will be evicted first
on memory pressure.
Use this to make sure surfaces and in particular non-dirty surfaces are
evicted first. Evicting in particular shaders, cotables and contexts imply
a significant performance hit on vmwgfx, so make sure these resources are
evicted last.
Some buffer objects are sub-allocated in user-space which means we can have
many resources attached to a single buffer object or resource. In that case
the buffer object is given the highest priority of the attached resources.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Deepak Rawat <drawat@vmware.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>

drivers/gpu/drm/vmwgfx/vmwgfx_surface.c

@@ -112,6 +112,8 @@ static const struct vmw_res_func vmw_legacy_surface_func = {
 	.res_type = vmw_res_surface,
 	.needs_backup = false,
 	.may_evict = true,
+	.prio = 1,
+	.dirty_prio = 1,
 	.type_name = "legacy surfaces",
 	.backup_placement = &vmw_srf_placement,
 	.create = &vmw_legacy_srf_create,
@@ -124,6 +126,8 @@ static const struct vmw_res_func vmw_gb_surface_func = {
 	.res_type = vmw_res_surface,
 	.needs_backup = true,
 	.may_evict = true,
+	.prio = 1,
+	.dirty_prio = 2,
 	.type_name = "guest backed surfaces",
 	.backup_placement = &vmw_mob_placement,
 	.create = vmw_gb_surface_create,