drm/i915/gem: Spring clean debugfs

Throw away all the debugfs entries that are not being actively used for
debugging/developing IGT. Note that a couple of these are already and
will remain available under the gt/

Files removed:
	i915_gem_fence_regs
	i915_gem_interrupt
	i915_ring_freq_table
	i915_context_status
	i915_llc
	i915_shrinker_info
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Andi Shyti <andi.shyti@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Andi Shyti <andi.shyti@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201202112140.16759-1-chris@chris-wilson.co.uk