dragon: rewrite the setup code

dragon: rewrite the setup code

We load the first ROM with an unpacking routine and all the data. On boot
it sets up the SAM (must be done from ROM), the PIAs and then says hello,
clears memory and moves all the RAM objects from a DECB stream we add
into the ROM image.

With that done, it flips to the second ROM which together with the
cartridge mappings gives you a high 32K for kernel code, although it has
to be split using text1/text2 as we must stuff the exception vectors into
0xBFF0-0xBFFF - so double check the fuzix.map