PR11671 Allocate __stp_tf_vma_entry dynamically.

PR11671 Allocate __stp_tf_vma_entry dynamically.

Get rid of TASK_FINDER_VMA_ENTRY_ITEMS and __stp_tf_vma_free_list_items
array list completely. All __stp_tf_vma_entry are allocated dynamically
now. This is possible since stap_add_vma_map_info() is only called
through the task_finder from a user context.

There is no more fixed maximum number of VMA pages that will be tracked
at runtime. This reduces memory use for those scripts that don't need any,
or only limited target process VMA tracking and allows easier system
wide probes inspecting shared library variables and/or user backtraces.
stap will now silently ignore -DTASK_FINDER_VMA_ENTRY_ITEMS.