Try to automatically fit sections into open spaces in the fixed area.

Try to automatically fit sections into open spaces in the fixed area.

Enhance layoutrom.py script to find and locate sections into fixed area.
Have layoutrom.py create output file instead of using redirect from make.
Don't use freespace2 for bios tables in f segment - freespace in fixed
    area is now automatically filled.
Change checkrom script to test final_code16_end instead of _start -
    this improves catching of alignment errors.
Don't align gdt to 8 bytes - it causes whole section to be aligned,
    which causes entry point to be misaligned.
Explicitly reserve space for variables in fixed area so that the space
    for them is not auto-filled.