tests/qtest: Ensure STM32L4x5 EXTI state is correct at the end of QTests

tests/qtest: Ensure STM32L4x5 EXTI state is correct at the end of QTests

EXTI's new field `irq_levels` tracks irq levels between tests when using
`global_qtest`.
This happens in `stm32l4x5_exti-test.c`, `stm32l4x5_syscfg-test.c` and
`stm32l4x5_gpio-test.c` (`dm163.c` doesn't use `global_qtest`).

To ensure that `irq_levels` has the same value before and after each
QTest, this commit toggles back the irq lines that were changed at the
end of each problematic test. Most QTests were already doing this.

Signed-off-by: Inès Varhol <ines.varhol@telecom-paris.fr>
Message-id: 20240629110800.539969-3-ines.varhol@telecom-paris.fr
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>