simplify and improve BOARD_USE_LEGACY_TOUCHSCREEN

in addition to converting ABS_MT_TOUCH_MAJOR to ABS_MT_PRESSURE, it also converts ABS_MT_WIDTH_MAJOR to ABS_MT_TOUCH_MAJOR.

also add 2 workarounds for some touchscreen driver which
 1. has BTN_TOUCH feature but it doesn't send BTN_TOUCH event
 2. sends multi-touch event for not-in-use pointer

Change-Id: I3a06b610f313fa27cfaf19b2edea37237533a28e
reference: http://source.android.com/tech/input/touch-devices.html