arm64: mvebu: extend the mmio region

Some of the setups including cn9130 opens mmio window starting from
0xc0000000, reflect it in the u-boot code.

Signed-off-by: Grzegorz Jaszczyk <jaz@semihalf.com>
Signed-off-by: Kostya Porotchkin <kostap@marvell.com>
Signed-off-by: Stefan Roese <sr@denx.de>