[POWERPC] Add of_find_matching_node() helper function

[POWERPC] Add of_find_matching_node() helper function

Similar to of_find_compatible_node(), of_find_matching_node() and
for_each_matching_node() allow you to iterate over the device tree
looking for specific nodes, except that they take of_device_id
tables instead of strings.

This also moves of_match_node() from driver/of/device.c to
driver/of/base.c to colocate it with the of_find_matching_node which
depends on it.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Paul Mackerras <paulus@samba.org>