mbv: small refactor interrupts

mbv/hal/intc.h

@@ -2,6 +2,8 @@
 
 #include <cstdint>
 
+namespace intc {
+
 using Isr = void(*)(void);
 
 /// Returns: true if the IRQ was previously enabled
@@ -14,3 +16,5 @@ void EnableInterrupts();
 
 // Feed this to the CPU's interrupt handler
 void InterruptHandler();
+
+}  // namespace intc