drm/i915/psr: Calculate and configure CUR_POS_ERLY_TPT

New register CUR_POS_ERLY_TPT related to early transport is
supposed to be configured when early transport is in use.

This register is used to configure cursor vertical postion
from beginning of selective update area.

Bspec: 68927

Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
Reviewed-by: Mika Kahola <mika.kahola@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231218175004.52875-5-jouni.hogander@intel.com