Input: psmouse - disable the synaptics extension on OLPC machines

OLPC has switched to a Synaptics touchpad.  It turns out that it's
pretty useless in absolute mode.  This patch looks for an OLPC
system (via DMI tables), and refuses to init Synaptics mode in
that scenario (falling back to relative mode).

Signed-off-by: Andres Salomon <dilinger@queued.net>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>