drm/nouveau/i2c/gf119-: add support for address-only transactions

Since switching the I2C-over-AUX helpers, there have been regressions on
some display combinations due to us not having support for "address only"
transactions.

This commits enables support for them for GF119 and newer.

Earlier GPUs have been reverted to a custom I2C-over-AUX algorithm.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drm/nouveau/i2c: transition pad/ports away from being based on nvkm_object

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>