cm3: nvic: use separate documentation to avoid warnings on cm0

Squelches some doxygen warnings, and makes the generated docs "right"
for each arch

lib/cm3/nvic.c

@@ -128,27 +128,27 @@ uint8_t nvic_get_irq_enabled(uint8_t irqn)
 	return NVIC_ISER(irqn / 32) & (1 << (irqn % 32)) ? 1 : 0;
 }
 
-/*---------------------------------------------------------------------------*/
+#if defined(__ARM_ARCH_7M__) || defined(__ARM_ARCH_7EM__)
 /** @brief NVIC Set Interrupt Priority
- *
- * CM3, CM4:
  *
  * There are 16 priority levels only, given by the upper four bits of the
  * priority byte, as required by ARM standards. The priority levels are
  * interpreted according to the pre-emptive priority grouping set in the
  * SCB Application Interrupt and Reset Control Register (SCB_AIRCR), as done
- * in @ref scb_set_priority_grouping.
- *
- * CM0:
+ * in @ref scb_set_priority_grouping,
+ * @param[in] irqn Interrupt number @ref CM3_nvic_defines_irqs
+ * @param[in] priority Interrupt priority (0 ... 255 in steps of 16)
+ */
+#else
+/** NVIC Set Interrupt Priority.
  *
  * There are 4 priority levels only, given by the upper two bits of the
  * priority byte, as required by ARM standards. No grouping available.
  *
- * @param[in] irqn Unsigned int8. Interrupt number @ref CM3_nvic_defines_irqs
- * @param[in] priority Unsigned int8. Interrupt priority (0 ... 255 in steps of
- * 16)
+ * @param[in] irqn Interrupt number @ref CM3_nvic_defines_irqs
+ * @param[in] priority Interrupt priority (0 ... 255 in steps of 16)
  */
-
+#endif
 void nvic_set_priority(uint8_t irqn, uint8_t priority)
 {
 	/* code from lpc43xx/nvic.c -- this is quite a hack and alludes to the