Allow compatibility with 'old' Touchscreens (Linux < 3.1)

BOARD_USE_LEGACY_TOUCHSCREEN := true in your BoardConfig.mk

Support the Multitouch, 10-points tested on the qtouch (Defy/Droid)

Remember to add the new idc file required for the touchscreen/keypad
Example: /system/usr/idc/qtouch-touchscreen.idc

Signed-off-by: Tanguy Pruvot <tanguy.pruvot@gmail.com>

 This is the 2nd commit message:

Legacy touchscreen: Fix B key issue

 This is the 3rd commit message:

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

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

Change-Id: I7b7f8802e45bf9d9f8de00373559a30ea839a178