drm/i915/skl+: pass skl_wm_level struct to wm compute func

This patch passes skl_wm_level structure itself to watermark
computation function skl_compute_plane_wm function (instead
of its internal parameters). It reduces number of arguments
required to be passed.

v2: Addressed review comments by Shashank Sharma

v3: Adding reviewed by tag from Shashank Sharma

v4: Added reviewed by from Juha-Pekka Heikkila

v5: Rebased the series

Reviewed-by: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com>
Reviewed-by: Shashank Sharma <shashank.sharma@intel.com>
Signed-off-by: Mahesh Kumar <mahesh1.kumar@intel.com>
Signed-off-by: Vidya Srinivas <vidya.srinivas@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1523245273-30264-7-git-send-email-vidya.srinivas@intel.com