[stm32] Enable flash cache by default

embassy-stm32/src/flash/mod.rs

@@ -178,3 +178,12 @@ cfg_if::cfg_if! {
     }
 }
 */
+
+// safety: must be called only once at startup
+pub(crate) unsafe fn init() {
+    crate::pac::FLASH.acr().modify(|w| {
+        w.set_dcen(true);
+        w.set_icen(true);
+        w.set_prften(true);
+    });
+}

embassy-stm32/src/lib.rs

@@ -161,6 +161,8 @@ pub fn init(config: Config) -> Peripherals {
         // must be after rcc init
         #[cfg(feature = "_time-driver")]
         time_driver::init();
+
+        flash::init();
     }
 
     p