i2c: designware: Disable device on system suspend

Userspace can initiate system suspend on arbitrary times which means that
device drivers must make sure that their device gets quiesced before system
suspend is entered. Therefore disable the I2C host controller in the driver
system suspend hook.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>