drm/i915/pmu: drop kernel-doc

The comments are closer to not being kernel-doc.

drivers/gpu/drm/i915/i915_pmu.h:21: warning: cannot understand function prototype: 'enum i915_pmu_tracked_events '
drivers/gpu/drm/i915/i915_pmu.h:32: warning: cannot understand function prototype: 'enum '
drivers/gpu/drm/i915/i915_pmu.h:41: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 * How many different events we track in the global PMU mask.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/7656b8f58b088c108a2a32f7089329740efabba1.1683041799.git.jani.nikula@intel.com