Input: bcm5974 - set the average number of events per MT event packet

The MT devices produce a lot of data. Tell the underlying input device
approximately how many events will be sent per synchronization, to allow
for better buffering. The number is a template based on continuously
reporting details for each finger on a single hand.

Signed-off-by: Henrik Rydberg <rydberg@euromail.se>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>