FROMGIT: drm/i915/d12+: Disable DMC handlers during loading/disabling the firmware

Disable the DMC event handlers before loading the firmware and after
uninitializing the display, to make sure the firmware is inactive. This
matches the Bspec "Sequences for Display C5 and C6" page for GEN12+.

Add a TODO comment for doing the same on pre-GEN12 platforms.

v2:
- Add a macro for the number of event handlers.
- Disable the event handlers only on GEN12+.
- s/dev_priv/i915/ in docbook comment.

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Uma Shankar <uma.shankar@intel.com> #v1
Link: https://patchwork.freedesktop.org/patch/msgid/20220728081440.1676857-1-imre.deak@intel.com
(cherry picked from commit fa6a4cde
 https://anongit.freedesktop.org/git/drm-intel.git

 drm-intel-next)

BUG=b:242077859
TEST=i915 driver loaded successfully

Change-Id: If4c8053212feaa0acdd8cd561e70bbda064a5c79
Signed-off-by: Mohanram Meenakshisundaram <mohanram.meenakshisundaram@intel.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/3910573


Reviewed-by: Rajat Jain <rajatja@google.com>
Reviewed-by: Drew Davenport <ddavenport@chromium.org>
Commit-Queue: Rajat Jain <rajatja@google.com>
Tested-by: Rajat Jain <rajatja@google.com>