Merge tag 'u-boot-stm32-20210715' of https://source.denx.de/u-boot/custodians/u-boot-stm

- DTS: alignment with Linux kernel v5.13 for stm32mp15 boards
- STM32MP1: update the stm32key command
- STM32MP1: activate the rng command
- STM32MP1: fix the stm32prog command (help, parttition size)
- STM32MP1: add fdtoverlay_addr_r variable
- STM32MP1: correctly managed SYSCON/SYSCFG clock
- STM32MP1: remove mmc alias and directly use device instance in boot_instance variable