Replace hardcoded memory map in kexec-fiwix with proper e820 passthrough

[Googulator]

Kexec-fiwix hardcodes the memory map used by qemu with the particular settings used in live-bootstrap. This can cause problems when bootstrapping on bare metal with a BIOS that reserves memory ranges that would be available in qemu, as well as preventing bootstrap on anything less than 4GB RAM, of which only 3GB ends up usable.

It would be much better if kexec-fiwix could actually query the BIOS using the real e820 mechanism, and pass the received mapping on to Fiwix (which then passes it to Linux).