drm/radeon/kms: i2c reorg

- keep the atom i2c id in the i2c rec
- fix gpio regs for GPIO and MDGPIO on pre-avivo chips
- track whether the i2c line is hw capable
- track whether the i2c line uses the multimedia i2c block

Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>