[platform][rosco-m68k] add proper support for the system data block
[platform][rosco-m68k] add proper support for the system data block

A block of data left behind by the firmware to tell the system important
things such as the size of memory.

littlekernel/lk,littlekernel/lk,hollanderic/lkstuff,littlekernel/lk,hollanderic/lkstuff,hollanderic/lkstuff,hollanderic/lkstuff,littlekernel/lk