Merge #792 #794

792: Add example for using a Signal. r=Dirbaio a=hydra

I didn't find an example, so I created one for the STM32H7.  Code based on the nrf mutex.rs example.

794: Fix F1 compilation by implementig AF pullup r=Dirbaio a=chemicstry

Embassy fails to compile on `STM32F103RET6`, because `set_as_af_pull` function is missing for GPIOv1:

```
error[E0599]: no method named `set_as_af_pull` found for mutable reference `&mut CLK` in the current scope
    --> C:\Users\chemi\.cargo\git\checkouts\embassy-0cff10c9b9902273\46473ae\embassy-stm32\src\sdmmc\mod.rs:1390:21
     |
1390 |             clk_pin.set_as_af_pull(clk_pin.af_num(), AFType::OutputPushPull, Pull::None);
     |                     ^^^^^^^^^^^^^^ method not found in `&mut CLK`
```

GPIOv1 actually supports pullups in AF mode, but only for inputs. The `sdmmc` driver, which was causing compile errors uses pullups for push-pull outputs and this will silently fail. But IMO not adding pullups to sdmmc interface is a hardware design problem, not HAL.

Co-authored-by: Dominic Clifton <me@dominicclifton.name>
Co-authored-by: chemicstry <chemicstry@gmail.com>
Co-authored-by: Dario Nieuwenhuis <dirbaio@dirbaio.net>