Merge #1376

1376: rtc: cleanup and consolidate r=Dirbaio a=xoviat

This removes an extra file that I left in, adds an example, and consolidates the files into one 'v2' file.

Co-authored-by: xoviat <xoviat@users.noreply.github.com>

embassy-stm32/src/lib.rs

@@ -51,7 +51,7 @@ pub mod pwm;
 pub mod qspi;
 #[cfg(rng)]
 pub mod rng;
-#[cfg(all(rtc, not(any(rtc_v1, rtc_v2f0, rtc_v2f7, rtc_v3, rtc_v3u5))))]
+#[cfg(all(rtc, not(rtc_v1)))]
 pub mod rtc;
 #[cfg(sdmmc)]
 pub mod sdmmc;