board/armltd/integrator/split_by_variant.sh: fix 'echo -n'

This patch fixes an error when running MAKEALL for ARM9.

On OS X /bin/sh uses builtin echo which does not utilise '-n' switch.
GNU manual for builtins recomend to use here-document style to solve
this portability issue.

This patch removes the usage of 'echo -n' and replace by here-document
style or a oneline echo command.

Signed-off-by: Andreas Bießmann <andreas.devel@googlemail.com>
CC: Peter Pearse <peter.pearse@arm.com>