i2c/of: Allow device node to be passed via i2c_board_info

The struct device_node *of_node pointer is moving out of dev->archdata
and into the struct device proper.  of_i2c.c needs to set the of_node
pointer before the device is registered.  Since the i2c subsystem
doesn't allow 2 stage allocation and registration of i2c devices, the
of_node pointer needs to be passed via the i2c_board_info structure
so that it is set prior to registration.

This patch adds of_node to struct i2c_board_info (conditional on
CONFIG_OF), sets of_node in i2c_new_device(), and modifies of_i2c.c
to use the new parameter.  The calling of dev_archdata_set_node()
from of_i2c will be removed in a subsequent patch when of_node is
removed from archdata and all users are converted over.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>