Support Bit Numbering for SPI

[Gentoli]

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Micros such as SAMD51 supports configuring SPI bit order.

There should be something exposed to make this configurable.

I think a good place for it could be here: https://github.com/rust-embedded/embedded-hal/blob/d45af5f9bf25e7e29029db578aaa3c10c35da424/src/spi.rs#L55 Adding an ordering enum to make this configurable.