base: clang-7 can't deduce non type parameter with auto

We now use explicit types instead (size_t)
This is fixing compiler checks, build 224 [1]

[1]: https://jenkins.gem5.org/job/compiler-checks/224/\
    artifact/compile-test-out/clang-version-7/

Change-Id: I5e94652b2fef554b1c47ce2972462401703ca5d5
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/59430
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Richard Cooper <richard.cooper@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>

src/base/memoizer.hh

@@ -141,7 +141,7 @@ class Memoizer
         });
     }
 
-    template <auto Start, auto End, auto Inc, class F>
+    template <size_t Start, size_t End, size_t Inc, class F>
     constexpr void
     iterateTupleArgs(F&& func)
     {