lib.kernel: make public

Remove the "version" parameter in order to make it more widely
available.
Starts making some kernel configuration helpers available.
The intent is to be able to better build and check the linux kernel
configuration.

pkgs/os-specific/linux/kernel/common-config.nix

@@ -16,10 +16,15 @@
 }:
 
 with stdenv.lib;
-
-  with import ../../../../lib/kernel.nix { inherit (stdenv) lib; inherit version; };
+with stdenv.lib.kernel;
 
 let
+  # Common patterns/legacy
+  whenAtLeast = ver: mkIf (versionAtLeast version ver);
+  whenOlder   = ver: mkIf (versionOlder version ver);
+  # range is (inclusive, exclusive)
+  whenBetween = verLow: verHigh: mkIf (versionAtLeast version verLow && versionOlder version verHigh);
+
 
   # configuration items have to be part of a subattrs
   flattenKConf =  nested: mapAttrs (_: head) (zipAttrs (attrValues nested));