staging: fsl-dpaa2/eth: Split function

Since setup_dpni() became a bit too long, move the buffer layout
configuration to a separate function.

Signed-off-by: Ioana Radulescu <ruxandra.radulescu@nxp.com>
Signed-off-by: Bogdan Purcareata <bogdan.purcareata@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>