Relocatable extracted RAM disk

[phaubertin]

Make extracted RAM disk relocatable by replacing pointers with relative offsets.

Rationale:

• We want the user space loader to pass the RAM disk location to the initial process so that process can map it in its own address space and use it.
• Future direction: we want to add the extracted RAM disk format as a supported RAM disk image format. Using this format uncompressed as the RAM disk image would allow the loader to use it in place so there wouldn't be two copies of the RAM disk in memory (original image + extracted). This would be useful for embedded systems with limited memory that run entirely off the initial RAM disk.