ACPI: APEI: GHES: Add helper to copy CPER CXL protocol error info to work struct

ACPI: APEI: GHES: Add helper to copy CPER CXL protocol error info to work struct

Make a helper out of cxl_cper_post_prot_err() that checks the CXL agent
type and copy the CPER CXL protocol errors information to a work data
structure.

Export the new symbol for reuse by ELOG.

Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Reviewed-by: Hanjun Guo <guohanjun@huawei.com>
Signed-off-by: Fabio M. De Francesco <fabio.m.de.francesco@linux.intel.com>
[ rjw: Subject tweak ]
Link: https://patch.msgid.link/20260114101543.85926-5-fabio.m.de.francesco@linux.intel.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>