drm/i915/display: Add DC5 counter and DMC debugfs entries for MTL

drm/i915/display: Add DC5 counter and DMC debugfs entries for MTL

MTL and dgfx use the same DC5 counter.

While at it, this patch also adds the corresponding
debugfs entries. Some cleanup wrt dc3co register
which makes the code more readable.

Driver loads all firmware that it finds in the firmware
binary but platform doesn't *need* all of them. Cleaning the
previous debugs entries to reflect which firmware is needed
and if the needed firmware is loaded or not.

MTL needs both Pipe A and Pipe B DMC to be loaded
along with Main DMC.

BSpec: 49788
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
Signed-off-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221010202135.28388-1-anusha.srivatsa@intel.com