ARM: DTS: add STM32F469 Discovery board support

This DT file comes from kernel v4.15-rc1

stm32f469-pinctrl.dtsi header has been updated with correct
STMicroelectronics Copyright.

Remove the paragraph about writing to the Free Software
Foundation's mailing address as requested by checkpatch.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>