riscv: ftrace: support PREEMPT

Now, we can safely enable dynamic ftrace with kernel preemption.

Signed-off-by: Andy Chiu <andy.chiu@sifive.com>
Reviewed-by: Björn Töpel <bjorn@rivosinc.com>
Link: https://lore.kernel.org/r/20250407180838.42877-9-andybnac@gmail.com
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com>

arch/riscv/Kconfig

@@ -157,7 +157,7 @@ config RISCV
 	select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
 	select HAVE_FUNCTION_GRAPH_TRACER if HAVE_DYNAMIC_FTRACE_WITH_ARGS
 	select HAVE_FUNCTION_GRAPH_FREGS
-	select HAVE_FUNCTION_TRACER if !XIP_KERNEL && !PREEMPTION
+	select HAVE_FUNCTION_TRACER if !XIP_KERNEL
 	select HAVE_EBPF_JIT if MMU
 	select HAVE_GUP_FAST if MMU
 	select HAVE_FUNCTION_ARG_ACCESS_API