Input: evdev - limit amount of data for writes

Limit amount of data that can be written into an evdev instance at
a given time to 4096 bytes (170 input events) to avoid holding
evdev->mutex for too long and starving other users.

Reviewed-by: Jeff LaBundy <jeff@labundy.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Link: https://lore.kernel.org/r/Zr5L8TUzkJcB9HcF@google.com


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>