m68k: Add more NeXT boot rom stuff

Those were found in the official headers in the NeXTstep ISO, how come I
didn't even look there in the first place?

We do get enough info to use the framebuffer, but sadly the SCSI IO
seems invalid. Both the NetBSD and even NeXTstep bootblock have their
own embedded drivers, maybe they didn't trust their own rom?

Change-Id: I0a47c433da89b15091644cd5c69ffff24d0cdd1f
Reviewed-on: https://review.haiku-os.org/c/haiku/+/3096
Reviewed-by: Alex von Gluck IV <kallisti5@unixzen.com>

m68k: add next_m68k boot platform

Since the boot ROM API structure is declared with a custom alignment, we
simulate it with padding bytes around, and use aligntest.prg to verify
using ARAnyM + TOS/MiNT as we know how to link simple PRG files.

It now prints something to the screen then panics when initializing the
heap.

For now one must insert the loader manually into an existing floppy
image:
dd if=generated-m68k/objects/haiku/m68k/release/system/boot/next_m68k/haiku_loader.next_m68k bs=$((0x8000)) seek=1 of=next_floppy.img conv=notrunc

Change-Id: I06d74e9d85a352aab68dedce545bbe5fe9e990d5
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2220
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>