ACPI: extlog: Fix finding the generic error data for v3 structure

Fix by using acpi_hest_get_payload() to find out the correct
generic error data for v3 structure.

The revision v300 generic error data is different from the old one, so
for compatibility with old and new version, change to a new interface to
locate the right memory error section that was defined in CPER.

Signed-off-by: Xiaochun Lee <lixc17@lenovo.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>