Raspberry Pi Pico HAL

[simon-77]

HAL implementation for the Raspberry Pi Pico Microcontroller.

• SPI implementation is tested using hardware.
• I2C is not yet implemented. Only en empty framework is provided, as well as an precompiler warning
• An examples for using the lcdgfx library from a Raspberry Pi Pico prject via CMake is provided as well

A issue was created first with further explanations, as stated in the Pull Request Process:
#116 (comment)

[CLAassistant]

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[simon-77]

I have signed the CLA in github now, but does github recognize it correctly?