RAS/CEC: Rename count_threshold to action_threshold

... which is the better, more-fitting name anyway.

Tony:
 - make action_threshold u64 due to debugfs accessors expecting u64.
 - rename the remaining: s/count_threshold/action_threshold/g

Co-developed-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: linux-edac <linux-edac@vger.kernel.org>