toolchain-shar-template.sh: Make relocation optional.

If the buildsystem is copied into the sdk and its toolchain is to
be used, then the relocation provided in toolchain-shar-template.sh
isn't needed and will actually fail.

So break the relocation aspect out and essentially make it another
SDK_POST_INSTALL_COMMAND script.

Signed-off-by: Randy Witt <randy.e.witt@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>