drm/i915/icl: Ungate ddi clocks before IO enable

IO enable sequencing needs ddi clocks enabled.
These clocks will be gated at a later point in
the enable sequence.

v2: Fix the commit header (Uma)
v3: Remove the redundant read (Ville)

Fixes: 949fc52a

 ("drm/i915/icl: add pll mapping for DSI")
Signed-off-by: Vandita Kulkarni <vandita.kulkarni@intel.com>
Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1553513202-13863-1-git-send-email-vandita.kulkarni@intel.com
(cherry picked from commit c5b81a32

)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>