Add stm32 flash + bootloader support

* Add flash drivers for L0, L1, L4, WB and WL. Not tested for WB, but
should be similar to WL.
* Add embassy-boot-stm32 for bootloading on STM32.
* Add flash examples and bootloader examples
* Update stm32-data

embassy-stm32/src/lib.rs

@@ -50,6 +50,8 @@ pub mod i2c;
 
 #[cfg(crc)]
 pub mod crc;
+#[cfg(any(flash_l0, flash_l1, flash_wl, flash_wb, flash_l4))]
+pub mod flash;
 pub mod pwm;
 #[cfg(rng)]
 pub mod rng;