mvebu: ds414: Move cmd_syno into ds414 directory

mvebu: ds414: Move cmd_syno into ds414 directory

When we switch to including all linker lists in SPL it is important to
not include commands as that may lead to link errors due to other things
we have already discarded.  In this case as we don't have other common
code nor other Synology borads, move the cmd_syno.c file (which claims
to be ds414 specific anyways!) into the ds414 directory and only build
it for non-SPL builds.

Signed-off-by: Tom Rini <trini@konsulko.com>