fix: mvebu: Add SPI parameters for environment setup

Add definitions for CONFIG_ENV_SPI_BUS and CONFIG_ENV_SPI_CS
to Armada-388-GP board configuration

Signed-off-by: Konstantin Porotchkin <kostap@marvell.com>
Cc: Igal Liberman <igall@marvell.com>
Cc: Stefan Roese <sr@denx.de>
Signed-off-by: Stefan Roese <sr@denx.de>