In order to properly support 64-bit jobs as well as Bifrost, a number of
structures need to be moved around, split, etc. which requires a lot of
shuffling things around. I think this would probably be hard to untangle
from the actual new Bifrost bits, so I've left everything together in
one commit. The list of things changed includes:

- To save some space due to the larger pointers, vertex and tiler jobs
  no longer have the same layout (i.e. common fields like shader_meta,
  etc. no longer have the same offset). A few of the tiler-only fields
  and vertex-only fields now overlap. The tiler job structure is much
  larger than the vertex job structure, although most of the new fields
  are zero for the things I've tried so far. It's not clear whether this
  also also happens on Midgard 64-bit jobs. In addition, there is a new
  Bifrost-only fused job type, where the common fields in the beginning
  are shared. The end result is that there is now a common prefix,
  followed by tiler-only or vertex-only fields (or both, for Midgard),
  and then a common postfix.
- For Bifrost, we no longer have to make a special incomplete FBD just
  for vertex and tiler jobs. Instead, the relevant fields (tiler_meta
  and the scratchpad) have been moved out into separate structures, and
  removed from the FBD when not needed for fragment jobs.
- There is no Bifrost driver that uses the SFBD, so we need to decode
  the MFBD now.