socz80: ramtop has changed type

Start bringing socz80 back into line
socz80: config.h updates
socz80: start reworking MMU code for 16K banking model

Bank switching functions, and switchin/switchout looked at so far. The fork
copying code remains to be done. Here it definitely makes sense to use the
MMU page 17 logic, but we now need to do it in 16K chunks.