cxl/events: Use a common struct for DRAM and General Media events

cxl/events: Use a common struct for DRAM and General Media events

cxl_event_common was an unfortunate naming choice and caused confusion with
the existing Common Event Record. Furthermore, its fields didn't map all
the common information between DRAM and General Media Events.

Remove cxl_event_common and introduce cxl_event_media_hdr to record common
information between DRAM and General Media events.

cxl_event_media_hdr, which is embedded in both cxl_event_gen_media and
cxl_event_dram, leverages the commonalities between the two events to
simplify their respective handling.

Suggested-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Alison Schofield <alison.schofield@intel.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Fabio M. De Francesco <fabio.m.de.francesco@linux.intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/20240607144423.48681-1-fabio.m.de.francesco@linux.intel.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>