Add SPI peripheral

[mciantyre]

Tracking issue for adding a SPI master implementation for the Teensy 4. The steps below are influenced by the work needed to bring-up an I2C master:

• [x] Add the LPSPI1 PAC subcrate to imxrt1062-pac.
  • If it's not already available, build the PAC supercrate, from which we'll import the LPSPI1 module as its own crate.
  • Import the module as its own crate using the import tool. Depends on #24.
• [x] Add IOMUXC pin configurations. It might look similar to some of the I2C work in 9dd4e90 and 26cfd09.
• [ ] Initialize SPI module (clocks, pin configurations, etc.)
• [ ] Implement embedded-hal traits
• [ ] Add docs
  • Update the pin muxing table in the teensy4-bsp docs
  • Document the module / API
• [ ] Add an example to the teensy4-examples. The behavior should be verifiable by someone with a logic analyzer.

[mciantyre]

Task 1 accomplished with #28.