dm: pinctrl: Skip gpio-controller node in pinconfig_post_bind()

dm: pinctrl: Skip gpio-controller node in pinconfig_post_bind()

Some binding define child node gpio-controller without compatible property.
This patch avoid to bind the pinconfig uclass to these node.

For example, the binding for st,stm32-pinctrl
(./device-tree-bindings/pinctrl/st,stm32-pinctrl.txt) defines the GPIO
controller/bank node as sub-node of pincontrol (st,stm32f429-pinctrl)
but without compatible (as it is not mandatory).

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>