powerpc/8610: add probing for individual DMA channels, not just DMA controllers

A future version of the MPC8610 HPCD's ASoC DMA driver will probe on individual
DMA channel nodes, so the DMA controller nodes' compatible string must be listed
in mpc8610_ids[] for the probe to work.

Also remove the "gianfar" compatible from mpc8610_ids[], since there is no
gianfar (or any other networking device) on the 8610.

Signed-off-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>