LoongArch: Add a default install.sh

As specified in scripts/install.sh, the priority order is as follows
(from highest to lowest):
  ~/bin/installkernel
  /sbin/installkernel
  arch/loongarch/boot/install.sh

Fallback to default install.sh if installkernel is not found.

Signed-off-by: Youling Tang <tangyouling@kylinos.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/boot/install.sh

@@ -0,0 +1,56 @@
+#!/bin/sh
+#
+# This file is subject to the terms and conditions of the GNU General Public
+# License.  See the file "COPYING" in the main directory of this archive
+# for more details.
+#
+# Copyright (C) 1995 by Linus Torvalds
+#
+# Adapted from code in arch/i386/boot/Makefile by H. Peter Anvin
+# Adapted from code in arch/i386/boot/install.sh by Russell King
+#
+# "make install" script for the LoongArch Linux port
+#
+# Arguments:
+#   $1 - kernel version
+#   $2 - kernel image file
+#   $3 - kernel map file
+#   $4 - default install path (blank if root directory)
+
+set -e
+
+case "${2##*/}" in
+vmlinux.elf)
+  echo "Installing uncompressed vmlinux.elf kernel"
+  base=vmlinux
+  ;;
+vmlinux.efi)
+  echo "Installing uncompressed vmlinux.efi kernel"
+  base=vmlinux
+  ;;
+vmlinuz.efi)
+  echo "Installing gzip/zstd compressed vmlinuz.efi kernel"
+  base=vmlinuz
+  ;;
+*)
+ echo "Warning: Unexpected kernel type"
+ exit 1
+ ;;
+esac
+
+if [ -f $4/$base-$1 ]; then
+  mv $4/$base-$1 $4/$base-$1.old
+fi
+cat $2 > $4/$base-$1
+
+# Install system map file
+if [ -f $4/System.map-$1 ]; then
+  mv $4/System.map-$1 $4/System.map-$1.old
+fi
+cp $3 $4/System.map-$1
+
+# Install kernel config file
+if [ -f $4/config-$1 ]; then
+  mv $4/config-$1 $4/config-$1.old
+fi
+cp .config $4/config-$1