[console] Try to avoid problems caused by keycode 86

[console] Try to avoid problems caused by keycode 86

The "us" keyboard layout contains a mapping for keycode 86 (which
seems not to correspond to any physical key on many US keyboards) to
the ASCII character '<'.  This mapping causes conflicts with the
mapping for keycode 51, which also maps (with shift) to '<'.

Change the keyboard mapping generator to choose the lowest keycode for
each ASCII character as indicating the relevant mapping to use, on the
basis that a lower keycode roughly indicates a "more normal" key.  On
a German keyboard, which has keys for both keycode 51 and keycode 86
present, this causes '<' to be remapped to ';', which is a closer
match to typical user expectations.

Reported-by: Sven Dreyer <sven@dreyer-net.de>
Signed-off-by: Michael Brown <mcb30@ipxe.org>