rtla: Make doc build optional

rtla build fails due to doc build dependency on rst2man. Make
doc build optional so rtla could be built without docs. Leave
the install dependency on doc_install alone.

Link: https://lkml.kernel.org/r/20220126001301.79096-1-skhan@linuxfoundation.orgAcked-by: NDaniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: NShuah Khan <skhan@linuxfoundation.org>
Signed-off-by: NSteven Rostedt (Google) <rostedt@goodmis.org>

tools/tracing/rtla/Makefile

@@ -59,7 +59,7 @@ endif
 .PHONY:	all
 all:	rtla
 
-rtla: $(OBJ) doc
+rtla: $(OBJ)
 	$(CC) -o rtla $(LDFLAGS) $(OBJ) $(LIBS)
 
 static: $(OBJ)