FROMGIT: drm/i915/dp: Add helpers to set link training mode, BW parameters

Add helpers to set the link mode and BW parameters. These are required
by a follow-up patch setting the parameters for a disabled link.

Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240722165503.2084999-9-imre.deak@intel.com
(cherry picked from commit 96c468c3
 https://gitlab.freedesktop.org/drm/i915/kernel.git

 drm-intel-next)

BUG=b:332903004, b:322223603
TEST=Verify the link training fallback for UHBR<->non-UHBR rates

Change-Id: I9423670f8ed468b238a450e4ff76d5c9178cd483
Signed-off-by: Rakshith M O <rakshith.m.o@intel.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/5802907


Reviewed-by: Manasi Navare <navaremanasi@chromium.org>
Reviewed-by: Sean Paul <sean@poorly.run>
Signed-off-by: Hubert Mazur <hmazur@google.com>