drm/i915: Stop forcing clock gating init for future platforms

drm/i915: Stop forcing clock gating init for future platforms

In the early days of i915, pretty much every platform needed to
initialize _something_ in the clock gating init functions.  In some
cases the items initialized were inside the GT (and really should have
been initialized through the GT workaround infrastructure instead).
In other cases they were display programming (sometimes not even related
to "clock gating" at all!) which probably needs to move inside the
display-specific code.  The number of initialization tasks that are
truly "clock gating" and don't fall within the GT or display domains is
relatively limited.  Let's stop forcing future platforms to always
define a clock gating init hook.

Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230906234732.3728630-7-matthew.d.roper@intel.com