Add support for enabling ram in 0xc0000-0xf0000 area.

Add support for enabling ram in 0xc0000-0xf0000 area.

Enhance shadow ram support to enable read/write of option rom area.
This enables support for option roms that modify themselves.
Support copying the roms before enabling shadowing, to work around the
    qemu implementation of ram shadowing.
Rename next_rom to RomEnd and export it.
Support locking ram being used for optionroms before booting.
Don't bother and'ing/or'ing 0x59 register - it's usage is well defined.