bsps: Support .rtemsstack.* linker input sections

Use a dedicated memory region or place it between the BSS and workspace.

Update #3459.

bsps/sparc/shared/start/linkcmds.base

@@ -154,6 +154,9 @@ SECTIONS
       *(.rela.rtemsroset*)
       *(.rela.rtemsrwset*)
     } >ram
+  .rtemsstack (NOLOAD) : {
+    *(SORT(.rtemsstack.*))
+  } > ram
   .data :
   {
     data_start = .;