package/opkg-utils: add opkg-utils as target pkg

package/opkg-utils: add opkg-utils as target pkg

Supports a use case of building container rootfs images where a matching
target version of the tools is required for repackaging of a installer
archive.

binutils binaries are needed for 'ar'; binutils does not work on nios2,
but busybox does, and so we can have 'ar' on nios2 with busybox.

A few other compressors can be used besides gzip, but the default in the
scripts is gzip, so we only ensure this one is enabled. Users who want
other compressors will have to enable them in their configurations.

Note: the order of 'select' is not strictly alphabetical: all packages
provided by busybox applets have been grouped together at the top, with
packages never provided by busybox applets together at the end.

Signed-off-by: Ryan Barnett <ryan.barnett@rockwellcollins.com>
[yann.morin.1998@free.fr:
  - only select full-blown packages if busybox is not enabled
  - select BR2_PACKAGE_BUSYBOX_SHOW_OTHERS, instead of 'depends on'
  - allow on nios2 when busybox is enabled
  - add binutils binaries on target (for 'ar')
  - drop _DEPENDENCIES: they all are only runtime-dpeendencies
  - add comment when python(2) is enabled
]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>