Merge tag 'xilinx-for-v2021.04-v2' of https://gitlab.denx.de/u-boot/custodians/u-boot-microblaze

Xilinx changes for v2021.04-v2

env:
- Unlock redundant variable configuration for all

xilinx:
- Enable seps525 by default
- Export bootseq via variable
- Update board_fdt_blob_setup()

mmc:
- Xenon macro removal