m68k: write bootinfo as rom section and re-randomize on reboot

m68k: write bootinfo as rom section and re-randomize on reboot

Rather than poking directly into RAM, add the bootinfo block as a proper
ROM, so that it's restored when rebooting the system. This way, if the
guest corrupts any of the bootinfo items, but then tries to reboot,
it'll still be restored back to normal as expected.

Then, since the RNG seed needs to be fresh on each boot, regenerate the
RNG seed in the ROM when reseting the CPU.

Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Message-Id: <20221023191340.36238-1-Jason@zx2c4.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>