Only export Interrupt as interrupt when 'rt' is enabled

It only makes sense to export interrupt if the interrupt! macro is
exported as well, since it's the only thing using it.

Author: rnestler

src/generate/device.rs

@@ -119,6 +119,7 @@ pub fn render(d: &Device, target: &Target, nightly: bool, device_x: &mut String)
             pub use cortex_m::peripheral::Peripherals as CorePeripherals;
             #[cfg(feature = "rt")]
             pub use cortex_m_rt::interrupt;
+            #[cfg(feature = "rt")]
             pub use self::Interrupt as interrupt;
         });