fixed a few things with tilemaps
added 320x240 and 400x300 kernel modes

These modes are a little special : only switch buffer every other line
look for vga_odd for an odd line, youe vga_line will be called once
with it false and one with it true for each line.

- add them in kconf
- update simple modes to use them
- update simple engine to use them
- update emulator for it (issues fake lines)

/!\ still an issue : spreading the engine load in two lines does not
work yet.