spl: remove forced linking of commands into SPL

spl: remove forced linking of commands into SPL

Remove linker command line options from the SPL makefile
that force the inclusion of unreferenced command code from
linked object files. As commands are not used in the SPL,
these options resulted in an unnecessary increase in the
image size, in addition to introducing the possibility of
tricky link errors in the case where the command code
contained symbols that were not resolved by linking in the
limited objects compiled in the SPL build.

Signed-off-by: Tyler Olmstead <tyler.j.olmstead@gmail.com>
Acked-by: Tom Rini <trini@ti.com>