pinctrl: stm32: protect configuration registers with a hwspinlock

If a hwspinlock if defined in device tree use it to protect
configuration registers.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@st.com>
Acked-by: Alexandre TORGUE <alexandre.torgue@st.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>