This command is supported only by v1 images and specifies a milliseconds
delay after executing some set of DATA commands. The special string value
SDRAM_SETUP instructs BootROM to setup SDRAM controller instead of
executing delay. SDRAM_SETUP may be specified only once and after the
last DATA command.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Marek Behún <marek.behun@nic.cz>
Reviewed-by: Chris Packham <judge.packham@gmail.com>
Reviewed-by: Stefan Roese <sr@denx.de>
Tested-by: Chris Packham <judge.packham@gmail.com>