of_i2c: Honour "status=disabled" property of device

Currently of_i2c_register_devices() function registers all i2c devices,
independently from their status property in device tree. According to
"ePAPR 1.1" spec, device should only be registered if there is no
"status" property, or it has "ok" (or "okay") value (see
of_device_is_available()). In case of "platform devices",
of_platform_device_create_pdata() checks for "status" and ensures
that disabled devices are not populated. But such check for i2c buses
was missing until now. Fix it.

Signed-off-by: Alexander Sverdlin <alexander.sverdlin@sysgo.com>
Acked-by: Rob Herring <robherring2@gmail.com>
Acked-by: Wolfram Sang <w.sang@pengutronix.de>
Reviewed-by: Barry Song <Baohua.Song@csr.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>