Add support of stm32mp135f discovery board (part number: STM32MP135F-DK).
It embeds a STM32MP135F SOC with 512 MB of DDR3.
Several connections are available on this board:
    4*USB2.0, 1*USB2.0 typeC DRD, SDcard, 2*RJ45, HDMI, Combo Wifi/BT, ...

Only SD card, uart4 (console) and watchdog IPs are enabled in this commit.
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>