drivers: display: ssd16xx: implement display_set_orientation API

I chose this approach instead of software rotation because I need it for
an ultra low power project.
Rotation in steps of 0, 90, 180, 270 degrees is done by changing
the data entry modes.
This commit removes the orientation-flipped property as it is redundant.

I made the assumption that the current driver implementation is right
about controller X/Y versus display width/height. The display controller X
parameter matches with the display height (dts) and display controller Y
parameter matches with the display width (dts). It looks like display
manufacturers choose to have it like this because a wider screen probably
makes more sense.

Tested on the reel_board with a 250x122 display (ssd1673 controller)
and a custom PCB with a 200x200 display (ssd1681 controller).
Also tested all orientations with various width/height dts overrides.

Signed-off-by: Sven Depoorter <svndepoorter@gmail.com>