ftrace: Make DYNAMIC_FTRACE always enabled for architectures that support it

ftrace has two flavors:

1) static: Where every function always calls the ftrace trampoline

2) dynamic: Where each function has nops that can be changed on demand to
jump to the ftrace trampoline when needed.

The static flavor has very high performance overhead and was only created
to make it easier for architectures to implement the dynamic flavor. An
architecture developer can first implement the static ftrace to make sure
the trampolines work before working on the more complicated dynamic aspect
of ftrace. Once the architecture can support dynamic ftrace, there's no
reason to continue to support the static flavor. In fact, the static
flavor tends to bitrot and bugs start to appear in them.

Remove the prompt to pick DYNAMIC_FTRACE and simply enable it if the
architecture supports it.

Link: https://lore.kernel.org/all/[e-mail]/

Cc: Masami Hiramatsu <[e-mail]>
Cc: Mathieu Desnoyers <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Alexandre Ghiti <[e-mail]>
Cc: ChenMiao <[e-mail]>
Link: https://lore.kernel.org/[e-mail]
Signed-off-by: Steven Rostedt (Google) <[e-mail]>

kernel/trace/Kconfig

···
 	  funcgraph-args (for the function graph tracer)
 
 config DYNAMIC_FTRACE
-	bool "enable/disable function tracing dynamically"
+	bool
 	depends on FUNCTION_TRACER
 	depends on HAVE_DYNAMIC_FTRACE
 	default y