x86/entry: Make enter_from_user_mode() static

The ASM users are gone. All callers are local.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Andy Lutomirski <luto@kernel.org>
Link: https://lore.kernel.org/r/20200521202120.129232680@linutronix.de

arch/x86/entry/common.c

@@ -56,7 +56,7 @@
  * 2) Invoke context tracking if enabled to reactivate RCU
  * 3) Trace interrupts off state
  */
-__visible noinstr void enter_from_user_mode(void)
+static noinstr void enter_from_user_mode(void)
 {
 	enum ctx_state state = ct_state();