hw/gpio: Implement STM32L4x5 GPIO

Features supported :
- the 8 STM32L4x5 GPIOs are initialized with their reset values
    (except IDR, see below)
- input mode : setting a pin in input mode "externally" (using input
    irqs) results in an out irq (transmitted to SYSCFG)
- output mode : setting a bit in ODR sets the corresponding out irq
    (if this line is configured in output mode)
- pull-up, pull-down
- push-pull, open-drain

Difference with the real GPIOs :
- Alternate Function and Analog mode aren't implemented :
    pins in AF/Analog behave like pins in input mode
- floating pins stay at their last value
- register IDR reset values differ from the real one :
    values are coherent with the other registers reset values
    and the fact that AF/Analog modes aren't implemented
- setting I/O output speed isn't supported
- locking port bits isn't supported
- ADC function isn't supported
- GPIOH has 16 pins instead of 2 pins
- writing to registers LCKR, AFRL, AFRH and ASCR is ineffective

Signed-off-by: Arnaud Minier <arnaud.minier@telecom-paris.fr>
Signed-off-by: Inès Varhol <ines.varhol@telecom-paris.fr>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Message-id: 20240305210444.310665-2-ines.varhol@telecom-paris.fr
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

docs/system/arm/b-l475e-iot01a.rst

@@ -18,6 +18,7 @@ Currently B-L475E-IOT01A machine's only supports the following devices:
 - STM32L4x5 EXTI (Extended interrupts and events controller)
 - STM32L4x5 SYSCFG (System configuration controller)
 - STM32L4x5 RCC (Reset and clock control)
+- STM32L4x5 GPIOs (General-purpose I/Os)
 
 Missing devices
 """""""""""""""
@@ -25,7 +26,6 @@ Missing devices
 The B-L475E-IOT01A does *not* support the following devices:
 
 - Serial ports (UART)
-- General-purpose I/Os (GPIO)
 - Analog to Digital Converter (ADC)
 - SPI controller
 - Timer controller (TIMER)