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_timer/include/hardware/timer.h

@@ -144,6 +144,15 @@ void hardware_alarm_claim(uint alarm_num);
  */
 void hardware_alarm_unclaim(uint alarm_num);
 
+/*! \brief Determine if a hardware alarm has been claimed
+ *  \ingroup hardware_timer
+ *
+ * \param alarm_num the hardware alarm number
+ * \return true if claimed, false otherwise
+ * \see hardware_alarm_claim
+ */
+bool hardware_alarm_is_claimed(uint alarm_num);
+
 /*! \brief Enable/Disable a callback for a hardware timer on this core
  *  \ingroup hardware_timer
  *

src/rp2_common/hardware_timer/timer.c

@@ -28,6 +28,11 @@ void hardware_alarm_unclaim(uint alarm_num) {
     hw_claim_clear(&claimed, alarm_num);
 }
 
+bool hardware_alarm_is_claimed(uint alarm_num) {
+    check_hardware_alarm_num_param(alarm_num);
+    return hw_is_claimed(&claimed, alarm_num);
+}
+
 /// tag::time_us_64[]
 uint64_t time_us_64() {
     // Need to make sure that the upper 32 bits of the timer