display: add basic display control

While i am trying to solve the wakeup delay i noticed
that the panel driver uses different brightness values
for different phones (red / green lense).
With a small display control driver those values
can be easily exposed to userspace.
Green ones used to have 0x09, those colors looked a bit
washed out.

echo xx > /sys/class/misc/display_control/display_brightness_value

Where xx can be (theoretically) a value between 0 and 255.
0  will set the screen to almost 0,
9  will set the screen to some kind of blue-washed colors,
31 will set the screen to more warmer colors (new default).

I also changed the sequence in mapphone_panel_disable_local().
This solves the "distorted" screen for me and also the wakeup
delay *seems* to be solved.

Signed-off-by: Blechd0se <alex.christ@hotmail.de>