cmd: scsi: Group the command portion together, guard with !CONFIG_SPL_BUILD

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, the SCSI code needs a lot
of attention so for now just guard the command portions.

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