tools/memory-model: Expand the cheatsheet.txt notion of relaxed

This commit adds a key entry enumerating the various types of relaxed
operations.  While in the area, it also renames the relaxed rows.

[ paulmck: Apply Boqun Feng feedback. ]
Acked-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

tools/memory-model/Documentation/cheatsheet.txt

@@ -3,9 +3,9 @@
                                C  Self  R  W  RMW  Self  R  W  DR  DW  RMW  SV
                               --  ----  -  -  ---  ----  -  -  --  --  ---  --
 
-Store, e.g., WRITE_ONCE()            Y                                       Y
-Load, e.g., READ_ONCE()              Y                          Y   Y        Y
-Unsuccessful RMW operation           Y                          Y   Y        Y
+Relaxed store                        Y                                       Y
+Relaxed load                         Y                          Y   Y        Y
+Relaxed RMW operation                Y                          Y   Y        Y
 rcu_dereference()                    Y                          Y   Y        Y
 Successful *_acquire()               R                   Y  Y   Y   Y    Y   Y
 Successful *_release()         C        Y  Y    Y     W                      Y
@@ -17,14 +17,19 @@ smp_mb__before_atomic()       CP        Y  Y    Y        a  a   a   a    Y
 smp_mb__after_atomic()        CP        a  a    Y        Y  Y   Y   Y    Y
 
 
-Key:	C:	Ordering is cumulative
-	P:	Ordering propagates
-	R:	Read, for example, READ_ONCE(), or read portion of RMW
-	W:	Write, for example, WRITE_ONCE(), or write portion of RMW
-	Y:	Provides ordering
-	a:	Provides ordering given intervening RMW atomic operation
-	DR:	Dependent read (address dependency)
-	DW:	Dependent write (address, data, or control dependency)
-	RMW:	Atomic read-modify-write operation
-	SELF:	Orders self, as opposed to accesses before and/or after
-	SV:	Orders later accesses to the same variable
+Key:	Relaxed:  A relaxed operation is either READ_ONCE(), WRITE_ONCE(),
+		  a *_relaxed() RMW operation, an unsuccessful RMW
+		  operation, a non-value-returning RMW operation such
+		  as atomic_inc(), or one of the atomic*_read() and
+		  atomic*_set() family of operations.
+	C:	  Ordering is cumulative
+	P:	  Ordering propagates
+	R:	  Read, for example, READ_ONCE(), or read portion of RMW
+	W:	  Write, for example, WRITE_ONCE(), or write portion of RMW
+	Y:	  Provides ordering
+	a:	  Provides ordering given intervening RMW atomic operation
+	DR:	  Dependent read (address dependency)
+	DW:	  Dependent write (address, data, or control dependency)
+	RMW:	  Atomic read-modify-write operation
+	SELF:	  Orders self, as opposed to accesses before and/or after
+	SV:	  Orders later accesses to the same variable