add PICO_USE_FASTEST_SUPPORTED_CLOCK, and support vreg setting and SYS_CLOCK_MHZ=200 for rp2040#2285

kilograham merged 6 commits intodevelopraspberrypi/pico-sdk:developfrom

clock_voltage_and_speedraspberrypi/pico-sdk:clock_voltage_and_speedCopy head branch name to clipboard