ld: pru: Place exception-handling sections correctly

  * scripttempl/pru.sc (OUTPUT_SECTION_ALIGN): New helper variable to place at end of DMEM output sections.
  (.data): Use the helper variable.
  (.eh_frame): New output section.
  (.gnu_extab): Ditto.
  (.gcc_except_table): Ditto.
  (.resource_table): Use the helper variable.