Polish notos initialisation

Clean up any easily resolvable building site in the boot code, i.e. provide
the standard ignore_int interrupt handler (above 1 MiB) by default. I think
I'd like to tackle a keyboard driver now.

Correct e820 memory detection. It used 20 bytes buffers where other code
assumed 24 byte structures.

Display the "congrats" message and some useful information after everything
is in place. We have a bleeding new printf() routine that is capable of
scrolling the screen (but not thread-safe). I hope to not have to revisit
this code again except to add some formats and thread-safety :-) This was
the first time I missed C but a lot of fun nevertheless.

My tests showed that the stack is left intact with all the strings that are
printed so far. Inserting int $3 traps is handy with the 'qdebug' target to
examine the machine state at some points.

The #CPUs field from MEMORY wasn't set. Now it is.