net/mlx5: Update the driver with the recent thermal changes

The thermal framework is migrating to the generic trip points. The set
of changes also implies a self-encapsulation of the thermal zone
device structure where the internals are no longer directly accessible
but with accessors.

Use the new API instead, so the next changes can be pushed in the
thermal framework without this driver failing to compile.

No functional changes intended.

Cc: Sandipan Patra <spatra@nvidia.com>
Cc: Gal Pressman <gal@nvidia.com>
Cc: Saeed Mahameed <saeedm@nvidia.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Link: https://lore.kernel.org/r/20230525140135.3589917-2-daniel.lezcano@linaro.org