Make possible to define chip-select pin for internal SPI.
By defining chip-select pin, it's possible to start specific SPI device only.
This allows to have several same type of sensors on the same bus with different orientation.
This also simplifies the API a bit, since we anyway have to change the
drivers to pass additional information (the bus device index).
The orientation flag is merged with the rotation.
Jani Paalijarvi
Daniel Agar
David Sidrane
Beat Küng