Input: ALPS - fix trackstick detection on some Dell Latitudes

On some Dell Latitudes we fail to identify presence of trackstick unless we
reset the device. The issue is quite benign as we do perform reset in
alps_init(), so the trackstick ends up working, but mouse name reported to
userspace is not accurate.

In order to fix the issue while avoiding the additional lengthy reset we
move the resrt to alps_detect() and keep the discovered state to be used
later in alps_init().

Reported-by: Pali Rohár <pali.rohar@gmail.com>
Tested-by: Pali Rohár <pali.rohar@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>