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.
Chip-select and SPI initialization uses the new config, whereas the drivers
still use the existing defines.
The configuration in board_config.h can be removed after all drivers are
updated.
David Sidrane