drm: bridge: it66121: Add it66122 support

The it66121 and replaced with it66122. The part is register compatible
with what we have for it66121. pid 0x0612 on the 66121 device to
0x0622 on the 66122 device, but I guess it makes sense to someone.

Signed-off-by: Nishanth Menon <nm@ti.com>