Merge tag 'u-boot-stm32-20210209' of https://gitlab.denx.de/u-boot/custodians/u-boot-stm

- Enable the fastboot oem commands in stm32mp15 defconfig
- Fixes pinctrol for stmfx and stm32
- Add support of I2C6_K in stm32mp15 clock driver
- Alignment with Linux kernel device tree v5.11-rc2 for ST boards