feat(stm32_gpio): add a function to reset a pin

Add set_gpio_reset_cfg() to set a pin in its reset configuration:
analog, no-pull, speed low, and its secure configuration, thanks to
stm32_gpio_is_secure_at_reset().

Signed-off-by: Yann Gautier <yann.gautier@foss.st.com>
Change-Id: I7b73c3636859f97fcc57f81cf68b42efc727922e
diff --git a/plat/st/stm32mp1/stm32mp1_private.c b/plat/st/stm32mp1/stm32mp1_private.c
index 0165cfe..d7f3dd8 100644
--- a/plat/st/stm32mp1/stm32mp1_private.c
+++ b/plat/st/stm32mp1/stm32mp1_private.c
@@ -120,6 +120,15 @@
 	return bank * GPIO_BANK_OFFSET;
 }
 
+bool stm32_gpio_is_secure_at_reset(unsigned int bank)
+{
+	if (bank == GPIO_BANK_Z) {
+		return true;
+	}
+
+	return false;
+}
+
 unsigned long stm32_get_gpio_bank_clock(unsigned int bank)
 {
 	if (bank == GPIO_BANK_Z) {