dt2w: Add an option to enable doubletap2wake when on charger

The sys option "doubletap_charger" can have 3 values:
- 0 (default): no check on charger's presence;
- 1: same as default behaviour, but dt2w is also enable when charger is
  present;
- 2: dt2w is enabled only when charger is present.

Signed-off-by: Mikael Berthe <mikael@lilotux.net>
dt2w: Release TS events before suspend and on resume

Let's release the TS events on late resume when the touch device was
not suspended.  Hopefully it will fix casual extra touch events on wake
up.

Signed-off-by: Mikael Berthe <mikael@lilotux.net>
lge_touch_core: i2c_read: retry a few times before erroring out

Patch from Dennis Rassmann (showp1984) -- I've reduced the number of
retries to 4.

Initial commit message:

--
The i2c devices we are connecting to may not be ready yet, or just
busy. Retry with a 10ms pause in order to still obtain touch data.
This improves overall touch data robustness, but the main thing it
does:
WE CAN FINALLY GET TOUCH DATA IN SUSPEND ALL THE TIME.
--

Signed-off-by: Dennis Rassmann <showp1984@gmail.com>
Signed-off-by: Mikael Berthe <mikael@lilotux.net>
dt2w: Add an option to specify the dt2w touch area

The previous option doubletap_full_window is replaced with a more
generic option: "doubletap_area" can have 3 values:
- 0 (default): no check on touch area (i.e. full screen);
- 1: bottom area (left/right margins excluded);
- 2: top area (left/right margins excluded);
- 3: center of the screen.

Signed-off-by: Mikael Berthe <mikael@lilotux.net>
Remove old FIXMEs

Signed-off-by: Mikael Berthe <mikael@lilotux.net>
lge_touch_core.c: Remove unused global variable

Signed-off-by: Mikael Berthe <mikael@lilotux.net>
dt2w: Check the second tap is close to the first one

Signed-off-by: Mikael Berthe <mikael@lilotux.net>