ppc/pnv: Fix PNV I2C invalid status after reset

ppc/pnv: Fix PNV I2C invalid status after reset

The PNV I2C Controller was clearing the status register
after a reset without repopulating the "upper threshold
for I2C ports", "Command Complete" and the SCL/SDA input
level fields.

Fixed this for resets caused by a system reset as well
as from writing to the "Immediate Reset" register.

Fixes: 263b81ee15af ("ppc/pnv: Add an I2C controller model")
Signed-off-by: Glenn Miles <milesg@linux.vnet.ibm.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>