drm/i915: Move the TRANS_DDI_FUNC_CTL enable to a later point

No reason that I can see why we should enable TRANS_DDI_FUNC_CTL
before we set up the watermarks of configure the mbus stuff.
In fact reordering these seems to match the bspec sequence better,
and crucially will allow us to push the TRANS_DDI_FUNC_CTL enable
into the encoder enable hook as a followup.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200417134720.16654-2-ville.syrjala@linux.intel.com
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Jani Nikula <jani.nikula@intel.com>