Update MAX_CHANNELS definition

Make room to report pen and touch events simultaneously

Signed-off-by: Ping Cheng <pingc@wacom.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Clean up device_type initialization for tool on tablet

usbInitToolType retrieves device type from the kernel when tool
is on the tablet when X server starts. No need to do it again later.

Signed-off-by: Ping Cheng <pingc@wacom.com>
Acked-by: Chris Bagwell <chris@cnpbagwell.com>