board: freescale: t208xrdb: add a config option for rev D dts fixups

Under DM, we rely on u-boot's device tree to provide the correct PHY
addresses. The board_fix_fdt callback is intended to be used for
device tree fixups before relocation. Unfortunately, this isn't an
option when booting from flash since the device tree isn't writable
before relocation.

This patch introduces the CONFIG_T2080RDB_REV_D option to signal that a
board revision D or up is the target. The config option is used to set
the correct Aquantia PHY address in the board's u-boot device tree.

Defconfig files with the option enable explicitly are added for
convenience.

Signed-off-by: Camelia Groza <camelia.groza@nxp.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>