drm/i915: deprecate the i915.modeset module parameter

drm/i915: deprecate the i915.modeset module parameter

The i915.modeset parameter doesn't really provide any useful benefit
over the nomodeset kernel parameter. Anything that i915.modeset does can
be achieved via nomodeset or not probing i915 at all.

Unfortunately, the i915.modeset parameter is widely referenced on
various forums, and removing it is not that simple. Start off by
deprecating it in the module parameter documentation, and logging a
warning message on non-default values.

Cc: Daniel Veter <daniel.vetter@ffwll.ch>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/2c63e2048eed64f728478fbcfc84f51c7f3212e6.1724843853.git.jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>