drm/i915/display/psr2: Fix cursor updates using legacy apis

The fast path only updates cursor register what will not cause
any updates in the screen when using PSR2 selective fetch.

The only option that we have is to go through the slow patch that will
do full atomic commit, that will trigger the PSR2 selective fetch
compute and programing calls.

Without this patch is possible to see a mouse movement lag in Gnome
when PSR2 selective fetch is enabled.

Cc: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210717011227.204494-3-jose.souza@intel.com