drm/i915: Reinitialize sink scrambling/TMDS clock ratio on HPD

The LG 4k TV I have doesn't deassert HPD when I turn the TV off, but
when I turn it back on it will pulse the HPD line. By that time it has
forgotten everything we told it about scrambling and the clock ratio.
Hence if we want to get a picture out if it again we have to tell it
whether we're currently sending scrambled data or not. Implement
that via the encoder->hotplug() hook.

v2: Force a full modeset to not follow the HDMI 2.0 spec more
    closely (Shashank)

[pushed with whitespace fixes to make sparse happy]
Cc: Shashank Sharma <shashank.sharma@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180117192149.17760-1-ville.syrjala@linux.intel.com