Feature: Extend search paths for syslinux MBRs

Hi grml team,

attached you can find a PR to extend the search paths for the syslinux MBRs.
ArchLinux for example splits the support of BIOS, EFI 32-bit and 64-bit into different directories:
https://www.archlinux.org/packages/core/x86_64/syslinux/files/

Regards,
JoeKar