* Add missing DREQ_s
* store actual clock frequency in clock_configure (fixes#368)
* use dma DREQ values defined in dreqs/dma.h
* Fix hw_is_claimed, and add xxx_is_claimed APIs
* Add some PIO irq helper methods
* Add DMA channel IRQ status getter and clear methods
* Implement the correct PIO IRQ status/clear methods (good to have methods here as the h/w interrupt registers are super confusing)
* fix pico_multicore dependencies
* add missing wrapper func __aeabi_f2d
* Further DMA/PIO IRQ API cleanup (and review fixes)
* add PICO_INT64_OPS_IN_RAM flag
Adds a new cmsis_core INTERFACE library, which provides the basic CMSIS macros/definitions, and RP2040.h and system_RP2040.h
By default the isr_ methods in the vector table are renamed to their CMSIS versions, but this can be overridden by defining PICO_CMSIS_RENAME_EXCEPTIONS=0
