arm: socfpga: Guard commands with CONFIG_SPL_BUILD tests

In order for these commands to not be included in SPL we need to guard
compilation with CONFIG_SPL_BUILD checks.  Reorganize some sections of
code slightly in order to avoid new warnings and mark the command
functions as static as they should have been before.

Cc: Marek Vasut <marex@denx.de>
Signed-off-by: Tom Rini <trini@konsulko.com>