mmapphys: specify explicitly whether it's an allocate or map.

Previously, we distinguished that by using phys. address 0 as
the signal to allocate new physical memory. This stops working
if we want to map the beginning of the physical memory.
Added A_NORETURN to exit.
Bugfix: if there are no modes, we don't get another message.
Allow all I/O ports to be used.

Where did I have the information from that the range 0xF8..0xFF
is reserved?
Changed vesa/vga to use x86emu instead of vm86-mode.

That is, I moved vga and vesa into one application and added the
x86emu library plus some support code. This enables us to use
vesa on x86_64.
eco32+mmix: fixed keyboard driver.
eco32+mmix: fixed build by excluding slideshow.
Updated profiling.
Removed vm86-mode from the kernel.