initramfs: add default_cpio_list, and delete -d option support

When CONFIG_INITRAMFS_SOURCE is empty, the Makefile passes the -d
option to gen_initramfs.sh to create the default initramfs, which
contains /dev, /dev/console, and /root.

This commit simplifies the default behavior; remove the -d option,
and add the default cpio list.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

usr/gen_initramfs.sh

@@ -28,7 +28,6 @@ $0 [-o <file>] [-l <dep_list>] [-u <uid>] [-g <gid>] {-d | <cpio_source>} ...
 	<cpio_source>  File list or directory for cpio archive.
 		       If <cpio_source> is a .cpio file it will be used
 		       as direct input to initramfs.
-	-d             Output the default cpio list.
 
 All options except -o and -l may be repeated and are interpreted
 sequentially and immediately.  -u and -g states are preserved across
@@ -43,18 +42,6 @@ field() {
 	shift $1 ; echo $1
 }
 
-default_initramfs() {
-	cat <<-EOF >> ${output}
-		# This is a very simple, default initramfs
-
-		dir /dev 0755 0 0
-		nod /dev/console 0600 0 0 c 5 1
-		dir /root 0700 0 0
-		# file /kinit usr/kinit/kinit 0755 0 0
-		# slink /init kinit 0755 0 0
-	EOF
-}
-
 filetype() {
 	local argv1="$1"
 
@@ -263,9 +250,6 @@ while [ $# -gt 0 ]; do
 			[ "$root_gid" = "-1" ] && root_gid=$(id -g || echo 0)
 			shift
 			;;
-		"-d")	# display default initramfs list
-			default_initramfs
-			;;
 		"-h")
 			usage
 			exit 0