Flexible memory layout
These changes allow the Kernel and it's workspace be easily moved. The Kernel can be moved anywhere below 0x40000000 or above 0xC0000000 (there is still a requirement in the VDU driver). ZeroPage (+ ProcVecs) can be placed at any 64K aligned address.
This merge request makes no binary changes.
These changes are used to allow the Linux Port ROM image to be placed at location that avoids areas reserved by Linux.