stm32/gpio: make port G work on U5.

ci.sh

@@ -221,8 +221,8 @@ rm out/tests/stm32wb55rg/wpan_ble
 # unstable, I think it's running out of RAM?
 rm out/tests/stm32f207zg/eth
 
-# doesn't work. Wire in D0-D1 might be bad, or the special IOVDD2 PGx pins.
-rm out/tests/stm32u5a5zj/{gpio,usart*}
+# doesn't work, gives "noise error", no idea why. usart_dma does pass.
+rm out/tests/stm32u5a5zj/usart
 
 if [[ -z "${TELEPROBE_TOKEN-}" ]]; then
     echo No teleprobe token found, skipping running HIL tests

embassy-stm32/src/gpio.rs

@@ -763,6 +763,13 @@ pub(crate) unsafe fn init(_cs: CriticalSection) {
     <crate::peripherals::AFIO as crate::rcc::sealed::RccPeripheral>::enable_and_reset_with_cs(_cs);
 
     crate::_generated::init_gpio();
+
+    // Setting this bit is mandatory to use PG[15:2].
+    #[cfg(stm32u5)]
+    crate::pac::PWR.svmcr().modify(|w| {
+        w.set_io2sv(true);
+        w.set_io2vmen(true);
+    });
 }
 
 mod eh02 {