arm64: mvebu: Enable BUBT command support in A8K default config

Enable mvebu "bubt" command support in the default configuration
file for Armada-7040 and Armada-8040 development boards

Signed-off-by: Konstantin Porotchkin <kostap@marvell.com>
Cc: Stefan Roese <sr@denx.de>
Cc: Nadav Haklai <nadavh@marvell.com>
Cc: Neta Zur Hershkovits <neta@marvell.com>
Cc: Omri Itach <omrii@marvell.com>
Cc: Igal Liberman <igall@marvell.com>
Cc: Haim Boot <hayim@marvell.com>
Cc: Hanna Hawa <hannah@marvell.com>
Signed-off-by: Stefan Roese <sr@denx.de>