directdisk-bootloader-config.wks: Add example for custom bootloader config

Add new wks file as a example for a custom bootloader configuration.
This change also includes the configuration that file that will be
used.

This example is using syslinux with MBR, the configuration file is
almost the same as the one generated by wic. As stated before this
is just an example.

[YOCTO #8728]

(From OE-Core rev: 4a9db893f721c0da5d103d28b97a0302cc9e2197)

Signed-off-by: Mariano Lopez <mariano.lopez@linux.intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/lib/wic/canned-wks/directdisk-bootloader-config.cfg

@@ -0,0 +1,11 @@
+# This is an example configuration file for syslinux.
+PROMPT 0
+TIMEOUT 10
+
+ALLOWOPTIONS 1
+SERIAL 0 115200
+
+DEFAULT boot
+LABEL boot
+KERNEL /vmlinuz
+APPEND label=boot root=/dev/sda2 rootwait rootfstype=ext4 video=vesafb vga=0x318 console=tty0

scripts/lib/wic/canned-wks/directdisk-bootloader-config.wks

@@ -0,0 +1,10 @@
+# short-description: Create a 'pcbios' direct disk image with custom bootloader config
+# long-description: Creates a partitioned legacy BIOS disk image that the user
+# can directly dd to boot media. The bootloader configuration source is a user file.
+
+
+part /boot --source bootimg-pcbios --ondisk sda --label boot --active --align 1024
+part / --source rootfs --ondisk sda --fstype=ext4 --label platform --align 1024
+
+bootloader --configfile="directdisk-bootloader-config.cfg"
+