Parse the flat device tree for devices on Freescale SOC's that we know
about (gianfar, gianfar_mdio, i2c, mpc83xx_wdt).  We need to setup
platform devices and platform data for these devices to match arch/ppc
usage.

Also add a helper function (get_immrbase) that reports the base
address of the MMIO registers on the SOC.
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>