arm: socfpga: Enable SPL_DM_SEQ_ALIAS for all SOCFPGA configs

This feature is required in SPL to enable support for loading from SPI
flash.

Also clean up the #define in socfpga_common.h.

Signed-off-by: Nathan Rossi <nathan@nathanrossi.com>
Reviewed-by: Stefan Roese <sr@denx.de>
Acked: Marek Vasut <marex@denx.de>
Cc: Dinh Nguyen <dinguyen@opensource.altera.com>
Cc: Chin-Liang See <clsee@altera.com>
Cc: Marek Vasut <marex@denx.de>
Cc: Stefan Roese <sr@denx.de>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>