Merge tag 'u-boot-stm32-20201021' of https://gitlab.denx.de/u-boot/custodians/u-boot-stm

- Activate CMD_EXPORTENV/CMD_IMPORTENV/CMD_ELF for STM32MP15 defconfig
- Fix stm32prog command: parsing of FlashLayout without partition
- Update MAINTAINERS for ARM STM STM32MP
- Manage eth1addr on dh board with KS8851
- Limit size of cacheable DDR in pre-reloc stage in stm32mp1
- Use mmc_of_parse() to read host capabilities in mmc:sdmmc2 driver