ARM: dts: stm32: Add Stinger96 board support

ARM: dts: stm32: Add Stinger96 board support

Stinger96 is a 96Boards IoT Extended edition board designed and
manufactured by Shiratech solutions based on STM32MP1 SoC. Following
are the features of this board:

* 256MB DDR
* 125MB NAND Flash
* Onboard BG96 modem
* 1x uSD
* 2x USB (1 available as external connector and another connected to BG96)
* 1x SPI
* 1x PCM
* 2x UART (apart from serial console)
* 2x I2C (apart from one connected to PMIC)

Following peripherals are tested and known to work:

* BG96 modem
* 1x I2C (LS-I2C0)
* 1x SPI
* 1x UART (LS-UART0)
* USB (Only Gadget mode)
* uSD

More information about this board can be found in Shiratech website:
https://www.shiratech-solutions.com/products/stinger96/

Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>