use list of lists adoc from docs-resources

relates to:

* riscv/riscv-isa-manual#1532
* riscv/docs-resources#28

Signed-off-by: Kevin Broch <[email protected]>

src/spec-sample.adoc

@@ -38,17 +38,7 @@ endif::[]
 :footnote:
 :xrefstyle: short
 
-[preface]
-== List of figures
-list-of::image[hide_empty_section=true, enhanced_rendering=true]
-
-[preface]
-== List of tables
-list-of::table[hide_empty_section=true, enhanced_rendering=true]
-
-[preface]
-== List of listings
-list-of::listing[hide_empty_section=true, enhanced_rendering=true]
+include::../docs-resources/adoc/lists-of-ftl.adoc[]
 
 [WARNING]
 .This document is in the link:http://riscv.org/spec-state[Development state]