package/coreutils: allow building as individual binaries

package/coreutils: allow building as individual binaries

We add configuration option BR2_PACKAGE_COREUTILS_INDIVIDUAL_BINARIES
so that coreutils can be built and installed as individual binaries.
It can be used if the target file system doesn't support symlinks or
symlinks are undesirable.

The approach is modelled after Busybox's similarly named configuration
option.

Signed-off-by: Markus Mayer <mmayer@broadcom.com>
[Thomas: adjust to previous preparation commits.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>