cypress-touchkey : add sysfs interface to enable/disable lighting hardwarekey backlight on screen touch (Yank555.lu)

- include new CM philosophy of handling h/w keys backlight from the ROM (Yank555.lu)
- kept the old sysfs interface and handling for older ROMs (Yank555.lu)
- kept the sysfs interface to enable/disable lighting hardwarekey backlight on screen touch (Yank555.lu)

SysFS interface :

 * /sys/class/sec/sec_touchkey/touch_led_handling (rw)
 *
 *   0 - handled by ROM (newer CM10.2, default)
 *   1 - handled by kernel (older CM10.2)
 *
 * /sys/class/sec/sec_touchkey/touch_led_on_screen_touch (rw)
 *
 *   0 - hardware keys backlight only lights up if h/w keys are used
 *   1 - hardware keys backlight lights up if h/w keys are used or screen is touched (default)

Conflicts:
	drivers/input/keyboard/cypress/cypress-touchkey.c