arm64: mvebu: armada-8k: Only configure xHCI power on DB-88F7040 board

arm64: mvebu: armada-8k: Only configure xHCI power on DB-88F7040 board

This patch uses of_machine_is_compatible() to detect the board at runtime
and only configured the I2C IO expander for the xHCI power / reset on
the DB-88F7040 board. As this code will be used by other Armada-7k/8k
ports, its necessary to use this runtime detection here.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Nadav Haklai <nadavh@marvell.com>
Cc: Neta Zur Hershkovits <neta@marvell.com>
Cc: Kostya Porotchkin <kostap@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>