syslinux.bbclass: ensure creation of output directory
build_syslinux_cfg function creates syslinux configuration file.
The code assumes that the output directory exists, which is not
always the case. For example rm_work task removes rootfs directory
structure and causes build_syslinux_cfg to fail with this error:
Unable to open ../<image>-<version>/syslinux_vm.cfg
Made build_syslinux_cfg depend on output directory to ensure that
directory is created before running the function.
[YOCTO #10159]
Signed-off-by: Ed Bartosh <ed.bartosh@linux.intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
