[build] Use configured architecture in the GRUB config. (#18093)

- Why I did it
The existing grub configuration has a hardcoded "amd64" architecture in the kernel and initramfs names. This causes an error in the attempt to load the image compiled for a different architecture.

- How I did it
Use configured architecture in the GRUB config.

- How to verify it
Compile the image for Arm64 architecture and install it on the device.

installer/default_platform.conf

@@ -588,13 +588,13 @@ menuentry '$demo_grub_entry' {
         if [ x$grub_platform = xxen ]; then insmod xzio; insmod lzopio; fi
         insmod part_msdos
         insmod ext2
-        $GRUB_CFG_LINUX_CMD   /$image_dir/boot/vmlinuz-6.1.0-11-2-amd64 root=$grub_cfg_root rw $GRUB_CMDLINE_LINUX  \
+        $GRUB_CFG_LINUX_CMD   /$image_dir/boot/vmlinuz-6.1.0-11-2-${arch} root=$grub_cfg_root rw $GRUB_CMDLINE_LINUX  \
                 net.ifnames=0 biosdevname=0 \
                 loop=$image_dir/$FILESYSTEM_SQUASHFS loopfstype=squashfs                       \
                 systemd.unified_cgroup_hierarchy=0 \
                 apparmor=1 security=apparmor varlog_size=$VAR_LOG_SIZE usbcore.autosuspend=-1 $ONIE_PLATFORM_EXTRA_CMDLINE_LINUX
         echo    'Loading $demo_volume_label $demo_type initial ramdisk ...'
-        $GRUB_CFG_INITRD_CMD  /$image_dir/boot/initrd.img-6.1.0-11-2-amd64
+        $GRUB_CFG_INITRD_CMD  /$image_dir/boot/initrd.img-6.1.0-11-2-${arch}
 }
 EOF
 

installer/install.sh

@@ -141,6 +141,8 @@ if [ "$install_env" = "onie" ]; then
     onie_initrd_tmp=/
 fi
 
+arch="%%ARCH%%"
+
 # The build system prepares this script by replacing %%DEMO-TYPE%%
 # with "OS" or "DIAG".
 demo_type="%%DEMO_TYPE%%"

onie-mk-demo.sh

@@ -97,6 +97,7 @@ output_raw_image=$(eval echo $output_raw_image)
 
 # Tailor the demo installer for OS mode or DIAG mode
 sed -i -e "s/%%DEMO_TYPE%%/$demo_type/g" \
+       -e "s/%%ARCH%%/$arch/g" \
        -e "s/%%IMAGE_VERSION%%/$image_version/g" \
        -e "s/%%ONIE_IMAGE_PART_SIZE%%/$onie_image_part_size/" \
        -e "s/%%EXTRA_CMDLINE_LINUX%%/$EXTRA_CMDLINE_LINUX/" \