drm/vmwgfx: Remove ttm object hashtable

The object_hash hashtable for ttm objects is not being used.
Remove it and perform refactoring in ttm_object init function.

Signed-off-by: Maaz Mombasawala <mombasawalam@vmware.com>
Reviewed-by: Zack Rusin <zackr@vmware.com>
Reviewed-by: Martin Krastev <krastevm@vmware.com>
Signed-off-by: Zack Rusin <zackr@vmware.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221022040236.616490-5-zack@kde.org