arm: mvebu: Select SPL_DM_SEQ_ALIAS

Select SPL_DM_SEQ_ALIAS which is required for certain uclasses,
specifically SPI Flash.

Signed-off-by: Nathan Rossi <nathan@nathanrossi.com>
Reviewed-by: Stefan Roese <sr@denx.de>
Cc: Albert Aribaud <albert.u.boot@aribaud.net>
Cc: Stefan Roese <sr@denx.de>
Acked-by: Stefan Roese <sr@denx.de>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>