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: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Steven 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)