Merge branch 'master' of https://source.denx.de/u-boot/custodians/u-boot-marvell

CI: https://dev.azure.com/sr0718/u-boot/_build/results?buildId=379&view=results

- mvebu: Disable JFFS2 support for Kirkwood and Armada XP boards (Tony)
- kirkwood: Enable bootstd for Sheevaplug board (Tony)
- mvebu: Add Allied Telesis x250 board (Chris)
- mvebu: Updates for Allied Telesis boards (Chris)