kbuild: deb-pkg: split debian/copyright from the mkdebian script

Copy debian/copyright instead of generating it by the 'cat' command.

I also updated '2018' to '2023' while I was here.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <n.schier@avm.de>

scripts/package/debian/copyright

+This is a packaged upstream version of the Linux kernel.
+
+The sources may be found at most Linux archive sites, including:
+https://www.kernel.org/pub/linux/kernel
+
+Copyright: 1991 - 2023 Linus Torvalds and others.
+
+The git repository for mainline kernel development is at:
+git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
+
+    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 dated June, 1991.
+
+On Debian GNU/Linux systems, the complete text of the GNU General Public
+License version 2 can be found in `/usr/share/common-licenses/GPL-2'.

scripts/package/mkdebian

@@ -188,26 +188,6 @@ $sourcename ($packageversion) $distribution; urgency=low
  -- $maintainer  $(date -R)
 EOF
 
-# Generate copyright file
-cat <<EOF > debian/copyright
-This is a packaged upstream version of the Linux kernel.
-
-The sources may be found at most Linux archive sites, including:
-https://www.kernel.org/pub/linux/kernel
-
-Copyright: 1991 - 2018 Linus Torvalds and others.
-
-The git repository for mainline kernel development is at:
-git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
-
-    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 dated June, 1991.
-
-On Debian GNU/Linux systems, the complete text of the GNU General Public
-License version 2 can be found in \`/usr/share/common-licenses/GPL-2'.
-EOF
-
 # Generate a control file
 cat <<EOF > debian/control
 Source: $sourcename
@@ -268,6 +248,7 @@ ARCH := ${ARCH}
 KERNELRELEASE := ${KERNELRELEASE}
 EOF
 
+cp "${srctree}/scripts/package/debian/copyright" debian/
 cp "${srctree}/scripts/package/debian/rules" debian/
 
 exit 0