Add backlight dimmer option

This is based on n5dim by @mzhou  https://github.com/mzhou/n5dim

Signed-off-by: flar2 <asegaert@gmail.com>
More gradual levels for backlight dimmer mod (based on @mzhou module)

Signed-off-by: flar2 <asegaert@gmail.com>
Backlight dimmer mod: more gradual transitions

Signed-off-by: flar2 <asegaert@gmail.com>
backlight: fix a bug where the screen would be completely dark or near darkness with backlight_dimmer enabled when the display dimmed. The brightness level can't be any lower than dev->min_brightness and previous code allowed that to happen, so fix it.

Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>
Signed-off-by: flar2 <asegaert@gmail.com>
backlight: clean the code.

Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>
Signed-off-by: flar2 <asegaert@gmail.com>
backlight: add minimum backlight brightness module param.

Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>
Signed-off-by: flar2 <asegaert@gmail.com>
backlight: scale max current when the brightness level is below 15 instead of using always 0.

Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>
Signed-off-by: flar2 <asegaert@gmail.com>
Increasing default readahead values
Adds sio scheduler by Miguel Boton <mboton@gmail.com>
    Tune deadline, readahead, ondemand, interactive.

Conflicts:
	include/linux/mm.h