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

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>