ACPI / APEI: Make GHES estatus header validation more user friendly

ghes_read_estatus() checks various lengths in the top-level header to
ensure the CPER records to be read aren't obviously corrupt.

Take the opportunity to make this more user-friendly, printing a
(ratelimited) message about the nature of the header format error.

Suggested-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: James Morse <james.morse@arm.com>
[ rjw: Add missing 'static' ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>