coreutils: handle merged usr folder

For targets prepared with a usr-move, coreutils should not be attempting
to move binaries from `usr/bin` to `bin`.

Signed-off-by: James Knight <james.knight@rockwellcollins.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Tested-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>