Add support for SPI module

[haata]

Needed features:

• Master mode
• Slave mode
• 4 CS
• SPI Modes
• Fixed Peripheral Select Mode
• Variable Peripheral Select Mode

https://docs.rs/embedded-hal/0.2.4/embedded_hal/spi/index.html https://docs.rs/embedded-hal/0.2.4/embedded_hal/blocking/spi/index.html

Should be similar to atsamd qspi (with only 2 data pins) https://github.com/atsamd-rs/atsamd/blob/master/hal/src/common/thumbv7em/qspi.rs

Later

• PDC
• DMAC
• Multiplexed CS (up to 15 total CS)