soc/lowrisc: Remove the remains of a LowRISC soc

Looks like we've got a race condition between commit ce8763fb with
Change-Id I4e3e715106a1a94381a563dc4a56781c35883c2d ("mb/lowrisc: Remove
the Nexys4DDR port") and commit 2e38dbe5 with Change-Id
I5524732f6eb3841e43afd176644119b03b5e5e27 ("riscv: update mtime
initialization"). Let's fix it.

Change-Id: I03c5860b27d04b6e1d7868ba8ea7b52d1075aa6a
Signed-off-by: Peter Lemenkov <lemenkov@gmail.com>
Reviewed-on: https://review.coreboot.org/29165
Reviewed-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Reviewed-by: Philipp Hug <philipp@hug.cx>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/lowrisc/lowrisc/mtime.c

@@ -1,22 +0,0 @@
-/*
- * This file is part of the coreboot project.
- *
- * Copyright (C) 2018 HardenedLinux
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; version 2 of the License.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- */
-
-#include <mcall.h>
-
-/* FIXME: This is an empty implementation, please improve */
-/* This function is used to initialize HLS()->time/HLS()->timecmp  */
-void mtime_init(void)
-{
-}