sched/core: Always inline __this_cpu_preempt_check()

Quite a few unnecessary instrumentation calls are generated via the
no-op __this_cpu_preempt_check() call, if it gets uninlined by the
compiler:

  vmlinux.o: warning: objtool: in_entry_stack+0x9: call to __this_cpu_preempt_check() leaves .noinstr.text section
  vmlinux.o: warning: objtool: default_do_nmi+0x10: call to __this_cpu_preempt_check() leaves .noinstr.text section
  vmlinux.o: warning: objtool: fpu_idle_fpregs+0x41: call to __this_cpu_preempt_check() leaves .noinstr.text section
  vmlinux.o: warning: objtool: kvm_read_and_reset_apf_flags+0x1: call to __this_cpu_preempt_check() leaves .noinstr.text section
  vmlinux.o: warning: objtool: lockdep_hardirqs_on+0xb0: call to __this_cpu_preempt_check() leaves .noinstr.text section
  vmlinux.o: warning: objtool: lockdep_hardirqs_off+0xae: call to __this_cpu_preempt_check() leaves .noinstr.text section
  vmlinux.o: warning: objtool: irqentry_nmi_enter+0x69: call to __this_cpu_preempt_check() leaves .noinstr.text section
  vmlinux.o: warning: objtool: irqentry_nmi_exit+0x32: call to __this_cpu_preempt_check() leaves .noinstr.text section
  vmlinux.o: warning: objtool: acpi_processor_ffh_cstate_enter+0x9: call to __this_cpu_preempt_check() leaves .noinstr.text section
  vmlinux.o: warning: objtool: acpi_idle_enter+0x43: call to __this_cpu_preempt_check() leaves .noinstr.text section
  vmlinux.o: warning: objtool: acpi_idle_enter_s2idle+0x45: call to __this_cpu_preempt_check() leaves .noinstr.text section

Mark it __always_inline.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Tony Lindgren <tony@atomide.com>
Tested-by: Ulf Hansson <ulf.hansson@linaro.org>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20230112195542.089981974@infradead.org

include/linux/percpu-defs.h

@@ -310,7 +310,7 @@ extern void __bad_size_call_parameter(void);
 #ifdef CONFIG_DEBUG_PREEMPT
 extern void __this_cpu_preempt_check(const char *op);
 #else
-static inline void __this_cpu_preempt_check(const char *op) { }
+static __always_inline void __this_cpu_preempt_check(const char *op) { }
 #endif
 
 #define __pcpu_size_call_return(stem, variable)				\