x86: add amd microcode entries to grub config

Create initrd enries for x86 images, that'll load amd microcode as early
as possible. Also remove the preinit script responsible for late load of
microcode.

Signed-off-by: Tomasz Maciej Nowak <tomek_n@o2.pl>

target/linux/x86/base-files/lib/preinit/02_load_x86_ucode

@@ -1,12 +0,0 @@
-#!/bin/sh
-# Copyright (C) 2018 OpenWrt.org
-
-do_load_x86_ucode() {
-	if grep -q AuthenticAMD /proc/cpuinfo; then
-		if [ -e "/sys/devices/system/cpu/microcode/reload" ]; then
-			echo 1 > /sys/devices/system/cpu/microcode/reload
-		fi
-	fi
-}
-
-boot_hook_add preinit_main do_load_x86_ucode