board: stm32mp1: Add Avenger96 board support

board: stm32mp1: Add Avenger96 board support

Add support for Avenger96 board from Arrow Electronics based on STM32MP157
MPU. This board is one of the Consumer Edition (CE) boards of the 96Boards
family and has the following features:

SoC: STM32MP157AAC
PMIC: STPMIC1A
RAM: 1024 Mbyte @ 533MHz
Storage: eMMC v4.51: 8 Gbyte
         microSD Socket: UHS-1 v3.01
Ethernet Port: 10/100/1000 Mbit/s, IEEE 802.3 Compliant
Wireless: WiFi 5 GHz & 2.4GHz IEEE 802.11a/b/g/n/ac
          Bluetooth®v4.2 (BR/EDR/BLE)
USB: 2x Type A (USB 2.0) Host and 1x Micro B (USB 2.0) OTG
Display: HDMI: WXGA (1366x768)@ 60 fps, HDMI 1.4
LED: 4x User LED, 1x WiFi LED, 1x BT LED

More information about this board can be found in 96Boards website:
https://www.96boards.org/product/avenger96/

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Patrice Chotard <patrice.chotard@st.com>