drm/i915: PSR: deprecate link_standby support for core platforms.

On Haswell and Broadwell with link in standby when exit event happens
between vblank and VSC packet, PSR exit on panel but DPA transmitter
still sends black pixel. When this condition hits, panel will intermittently
display black frame.

The known W/A for this case involve the of single_frame update
that isn't supported on Haswell and to be supported on Broadwell
3 other workarounds would be required. So it is better and safe to
just deprecate link_standby for now.

Also, link fully off saves more power than link_standby and afwk
no OEM is requesting link standby on VBT. There is no reason for that.

For Skylake let's just consider it behaves like Broadwell until
we prove otherwise.

v2: Fix commit message (Durga).

v3: Fix conflict with PSR2.

Reference: HSD: bdwgfx/1912559
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Durgadoss R <durgadoss.r@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>