Small API additions and minor fixes (#406)

* 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

src/rp2_common/hardware_clocks/clocks.c

@@ -112,7 +112,7 @@ bool clock_configure(enum clock_index clk_index, uint32_t src, uint32_t auxsrc,
     clock->div = div;
 
     // Store the configured frequency
-    configured_freq[clk_index] = freq;
+    configured_freq[clk_index] = (uint32_t)(((uint64_t) src_freq << 8) / div);
 
     return true;
 }