drm/i915/vdsc: Set VDSC PIC_HEIGHT before using for DP DSC

Currently, pic_height of vdsc_cfg structure is being used to calculate
slice_height, before it is set for DP.

So taking out the lines to set pic_height from the helper
intel_dp_dsc_compute_params() to individual encoders, and setting
pic_height, before it is used to calculate slice_height for DP.

Fixes: 5a6d866f ("drm/i915: Get slice height before computing rc params")
Cc: Manasi Navare <manasi.d.navare@intel.com>
Cc: Vandita Kulkarni <vandita.kulkarni@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Vandita Kulkarni <vandita.kulkarni@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220902103219.1168781-1-ankit.k.nautiyal@intel.com