Allow rom to grow beyond 64K.

Allow rom to grow beyond 64K.

If rom is over 64K then use part of e-segment for 32bit code.
Push 32bit code as high as it can go in the f-segment.
Do version building before layoutrom.py - this way layoutrom knows
    full size of rom.
Make layoutrom.py build the full ld script - remove now unused ld
    scripts that just imported the output of layoutrom.py.
Also, use "objdump" instead of "nm" - reduce toolchain requirements.
Enhance tools/checkrom.py so that it can pad bios.bin to size qemu is
    happy with.
Also, add dependencies to build rules for local tools - if tool
    changes automatically rerun it.
Make sure option roms don't overwrite the 32bit code (should the 32bit
    code be in the e-segment).
Make sure shadow code works even if part of the code is in the
    e-segment.