Documentation/admin-guide: Add bus lock ratelimit

Since bus lock rate limit changes the split_lock_detect parameter,
update the documentation for the change.
Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Link: https://lore.kernel.org/r/20210419214958.4035512-4-fenghua.yu@intel.com

Documentation/admin-guide/kernel-parameters.txt

@@ -5283,6 +5283,14 @@
 				  exception. Default behavior is by #AC if
 				  both features are enabled in hardware.
 
+			ratelimit:N -
+				  Set system wide rate limit to N bus locks
+				  per second for bus lock detection.
+				  0 < N <= 1000.
+
+				  N/A for split lock detection.
+
+
 			If an #AC exception is hit in the kernel or in
 			firmware (i.e. not while executing in user mode)
 			the kernel will oops in either "warn" or "fatal"