ACPI, x86/boot: Split out acpi_generic_reduce_hw_init() and export

This is a preparation patch to allow override the hardware reduced
initialization on ACPI enabled platforms.

No functional change intended.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J . Wysocki <rafael.j.wysocki@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-acpi@vger.kernel.org
Link: http://lkml.kernel.org/r/20180220180506.65523-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/include/asm/acpi.h

@@ -140,6 +140,8 @@ static inline u64 acpi_arch_get_root_pointer(void)
 	return x86_init.acpi.get_root_pointer();
 }
 
+void acpi_generic_reduced_hw_init(void);
+
 #else /* !CONFIG_ACPI */
 
 #define acpi_lapic 0
@@ -149,6 +151,8 @@ static inline void acpi_noirq_set(void) { }
 static inline void acpi_disable_pci(void) { }
 static inline void disable_acpi(void) { }
 
+static inline void acpi_generic_reduced_hw_init(void) { }
+
 #endif /* !CONFIG_ACPI */
 
 #define ARCH_HAS_POWER_INIT	1

arch/x86/kernel/acpi/boot.c

@@ -1376,17 +1376,21 @@ static int __init dmi_ignore_irq0_timer_override(const struct dmi_system_id *d)
  *
  * We initialize the Hardware-reduced ACPI model here:
  */
+void __init acpi_generic_reduced_hw_init(void)
+{
+	/*
+	 * Override x86_init functions and bypass legacy PIC in
+	 * hardware reduced ACPI mode.
+	 */
+	x86_init.timers.timer_init	= x86_init_noop;
+	x86_init.irqs.pre_vector_init	= x86_init_noop;
+	legacy_pic			= &null_legacy_pic;
+}
+
 static void __init acpi_reduced_hw_init(void)
 {
-	if (acpi_gbl_reduced_hardware) {
-		/*
-		 * Override x86_init functions and bypass legacy pic
-		 * in Hardware-reduced ACPI mode
-		 */
-		x86_init.timers.timer_init	= x86_init_noop;
-		x86_init.irqs.pre_vector_init	= x86_init_noop;
-		legacy_pic			= &null_legacy_pic;
-	}
+	if (acpi_gbl_reduced_hardware)
+		acpi_generic_reduced_hw_init();
 }
 
 /*