mdnie: toggling mdnie negative effect with home button

pressing home button 4 times will toggle screen negative effect. the delay between consecutive button presses should be less than 300 miliseconds.

Conflicts:
drivers/input/keyboard/gpio_keys.c

Change-Id: I07e60b2f935bca154ca965f080b5052b56528050

Conflicts:
drivers/video/samsung/mdnie.c
 input: gpio_keys: make homekey press count and max delay between pres…

…ses (to toggle mdnie negative effect) static variables to be able to configure them with kmemhelper
 input: gpio_keys: remove static modifier to make the variables modifi…

…able using kmemhelper, add enable/disable module parameter and also make homekey_trg_cnt reflect the number of presses by modifying the comparison (thanks to tungstwenty)