ARM: dts: Add support for stm32f746-evaluation board support

ARM: dts: Add support for stm32f746-evaluation board support

This board offers:
  _ STM32F746NGH6 microcontroller with 1 Mbyte Flash and 320+4 Kbytes RAM
  _ Six 5 V power supply options:
        Power jack
        ST-LINK/V2-1 USB connector
        User USB HS connector
        User USB FS1 connector
        User USB FS2 connector
        Daughterboard
  _ SAI Audio DAC, stereo audio jack which supports headset with microphone
  _ Stereo digital microphone, audio jack connector used to connect
    external speakers
  _ 2 Gbytes (or more) SDMMC interface microSD card
  _ RF-EEPROM on I2C compatible serial interface
  _ RS-232 communication
  _ IrDA transceiver
  _ JTAG/SWD and ETM trace debug support, ST-LINK/V2-1 embedded
  _ IEEE-802.3-2002 compliant Ethernet connector
  _ Camera module
  _ 8Mx32 bit SDRAM, 1Mx16 bit SRAM & 8Mx16 bit Nor Flash
  _ 512 Mbits QuadSPI Nor Flash
  _ 5.7 inch 640x480 pixel TFT color LCD with capacitive touch panel
  _ Joystick with 4-direction control and selector
  _ Reset, WakeUp/Tamper or key button
  _ 4 color user LEDs
  _ Extension connectors & memory connectors for daughterboard or
    wrapping board
  _ USB OTG HS and FS with Micro-AB connectors
  _ RTC with backup battery
  _ CAN 2.0A/B compliant connection
  _ Potentiometer
  _ Motor control connector

More detailed information are available here :
http://www.st.com/en/evaluation-tools/stm32746g-eval.html

To compile stm32f746-eval board, use same defconfig as
stm32f746-disco, the only difference is to pass
"DEVICE_TREE=stm32746g-eval".

Signed-off-by: Christophe Priouzeau <christophe.priouzeau@st.com>
Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Acked-by: Vikas Manocha <vikas.manocha@st.com>