ARM: STi: stih41x: Add support for the FSM Serial Flash Controller

Here we add the necessary device nodes required for successful device
probing and Pinctrl setup for the FSM when booting on an STiH415 (Orly1)
or STiH416 (Orly2) based b2020 development board.

Acked-by: Srinivas Kandagatla <srinivas.kandagatla@st.com>
Acked-by Angus Clark <angus.clark@st.com>
Acked-by: Brian Norris <computersforpeace@gmail.com>
Acked-by: Maxime Coquelin <maxime.coquelin@st.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>