drm/i915/psr: Fix intel_psr2_sel_fetch_et_alignment usage

Currently we are not aligning selective update area to cover cursor fully
when cursor is not updated by itself but still in the selective update
area. Fix this by checking cursor separately after
drm_atomic_add_affected_planes.

Bspec: 68927

Fixes: 1bff93b8

 ("drm/i915/psr: Extend SU area to cover cursor fully if needed")
Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
Reviewed-by: Mika Kahola <mika.kahola@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240319123327.1661097-4-jouni.hogander@intel.com