epyc: move to latest kernel for snappier performance

hosts/epyc.nix

@@ -1,4 +1,4 @@
-{ lib, ... }:
+{ lib, pkgs, ... }:
 let
   gcc-system-features = arch: lib.optionals (arch != null) ([ "gccarch-${arch}" ]
     ++ map (x: "gccarch-${x}") lib.systems.architectures.inferiors.${arch});
@@ -20,6 +20,9 @@ in
   boot.loader.systemd-boot.enable = true;
   boot.loader.efi.canTouchEfiVariables = true;
 
+  # We want to use EEVDF and AMD-related niceties.
+  boot.kernelPackages = pkgs.linuxPackages_latest;
+
   # Open public access to our PostgreSQL.
   services.postgresql.enableTCPIP = true;
   services.postgresql.authentication = ''