AP_HAL_PX4: added IRQ save/restore to hal.scheduler

these are used by RPM driver

libraries/AP_HAL_PX4/Scheduler.cpp

@@ -457,4 +457,23 @@ void PX4Scheduler::system_initialized()
     _initialized = true;
 }
 
+
+/*
+  disable interrupts and return a context that can be used to
+  restore the interrupt state. This can be used to protect
+  critical regions
+*/
+void *PX4Scheduler::disable_interrupts_save(void)
+{
+    return (void *)(uintptr_t)irqsave();
+}
+
+/*
+  restore interrupt state from disable_interrupts_save()
+*/
+void PX4Scheduler::restore_interrupts(void *state)
+{
+    irqrestore((irqstate_t)(uintptr_t)state);
+}
+
 #endif

libraries/AP_HAL_PX4/Scheduler.h

@@ -64,6 +64,18 @@ public:
 
     void create_uavcan_thread() override;
 
+    /*
+      disable interrupts and return a context that can be used to
+      restore the interrupt state. This can be used to protect
+      critical regions
+     */
+    void *disable_interrupts_save(void) override;
+
+    /*
+      restore interrupt state from disable_interrupts_save()
+     */
+    void restore_interrupts(void *) override;
+    
 private:
     bool _initialized;
     volatile bool _hal_initialized;