This commit includes the following cleanups:
- The macros `I2C_DEV_1_USED` and `SPI_DEV_1_USED` are now used with the values 0 and 1. This allows to enable but also to disable the second interface even if the board definition enables it by default.
- The second I2C device `I2C_DEV(1)` and the second SPI device `SPI_DEV(1)` are now disabled by default.
- The second SPI device `SPI_DEV(1)` now uses PB5 as default CS signal instead of PA4 to keep PA4 free for ADC or DAC even if `SPI_DEV(1)` is used, for example for the TFT display.
The default I2C device configuration allows to define up to two I2C devices `I2C_DEV(0)` and `I2C_DEV(1)`. `I2C_DEV(0)` is always defined if the I2C peripheral is enabled by the module `periph_spi`. The second I2C device `I2C_DEV(1)` is only defined if `I2C_DEV_1_USED` is defined by the board. This allows to use the default configuration with one or two I2C devices depending on whether other peripherals are enabled that would collide with the I2C devices.
