Re-adds embassy macros for stm32

* Hook RCC config into chip config and use chip-specific RCC init
  function
* RTC/clock setup is ignored for now

embassy-macros/src/chip/stm32.rs

@@ -0,0 +1,26 @@
+use crate::path::ModulePrefix;
+use proc_macro2::TokenStream;
+use quote::quote;
+
+pub fn generate(embassy_prefix: &ModulePrefix, config: syn::Expr) -> TokenStream {
+    let embassy_path = embassy_prefix.append("embassy").path();
+    let embassy_stm32_path = embassy_prefix.append("embassy_stm32").path();
+
+    quote!(
+        use #embassy_stm32_path::{clock::Clock};
+
+        let p = #embassy_stm32_path::init(#config);
+
+        /*
+        let mut rtc = #embass::RTC::new(unsafe { <peripherals::TIM2 as #embassy_path::util::Steal>::steal() }, interrupt::take!(TIM2));
+        let rtc = unsafe { make_static(&mut rtc) };
+        rtc.start();
+        let mut alarm = rtc.alarm0();
+
+        unsafe { #embassy_path::time::set_clock(rtc) };
+
+        let alarm = unsafe { make_static(&mut alarm) };
+        executor.set_alarm(alarm);
+        */
+    )
+}