Process the BTN_MOUSE event

This is required in order to make the trackball on devices that has it to
work properly, like it does before ICS. In addition to this patch, you just
need an .idc file that matches the device name for your the trackball. You can
find it by either looking in a kernel log or a logcat.

For example, a device with a Crucial optical navigation pad, will be called
curcial-oj.idc

The .idc file should contain the following:

cursor.mode = navigation
cursor.orientationAware = 1

Place the file in /system/usr/idc folder.

Enable in BoardConfig.mk with BOARD_USE_LEGACY_TRACKPAD := true

Change-Id: I57e9912b9e4d6242c980c99f4fd28b0d50f19bb8