ppc/pnv: Use resettable interface to reset child I2C buses

ppc/pnv: Use resettable interface to reset child I2C buses

The QEMU I2C buses and devices use the resettable
interface for resetting while the PNV I2C controller
and parent buses and devices have not yet transitioned
to this new interface and use the old reset strategy.
This was preventing the I2C buses and devices wired
to the PNV I2C controller from being reset.

The short term fix for this is to have the PNV I2C
Controller's reset function explicitly call the resettable
interface function, bus_cold_reset(), on all child
I2C buses.

The long term fix should be to transition all PNV parent
devices and buses to use the resettable interface so that
all child buses and devices are automatically reset.

Reviewed-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Glenn Miles <milesg@linux.vnet.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>