dm: gpio: Rename set_dir_flags() method to update_flags()

The current method is a misnomer since it is also used (e.g. by stm32) to
update pull settings and open source/open drain.

Rename it and expand the documentation to cover a few more details.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Pratyush Yadav <p.yadav@ti.com>

Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
diff --git a/drivers/gpio/stm32_gpio.c b/drivers/gpio/stm32_gpio.c
index 7184db3..6d1bef6 100644
--- a/drivers/gpio/stm32_gpio.c
+++ b/drivers/gpio/stm32_gpio.c
@@ -191,8 +191,8 @@
 	return GPIOF_FUNC;
 }
 
-static int stm32_gpio_set_dir_flags(struct udevice *dev, unsigned int offset,
-				    ulong flags)
+static int stm32_gpio_set_flags(struct udevice *dev, unsigned int offset,
+				ulong flags)
 {
 	struct stm32_gpio_priv *priv = dev_get_priv(dev);
 	struct stm32_gpio_regs *regs = priv->regs;
@@ -270,7 +270,7 @@
 	.get_value		= stm32_gpio_get_value,
 	.set_value		= stm32_gpio_set_value,
 	.get_function		= stm32_gpio_get_function,
-	.set_dir_flags		= stm32_gpio_set_dir_flags,
+	.set_flags		= stm32_gpio_set_flags,
 	.get_dir_flags		= stm32_gpio_get_dir_flags,
 };