ACPI: APEI: Silence missing prototype warnings

Silence the following warnings when make W=1:

 | CC   drivers/acpi/apei/apei-base.c
 |      warning: no previous prototype for 'arch_apei_enable_cmcff' [-Wmissing-prototypes]
 |              int __weak arch_apei_enable_cmcff(struct acpi_hest_header *hest_hdr,
 |                         ^
 | CC   drivers/acpi/apei/apei-base.c
 |      warning: no previous prototype for 'arch_apei_report_mem_error' [-Wmissing-prototypes]
 |              void __weak arch_apei_report_mem_error(int sev,
 |                          ^
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/apei/apei-base.c

@@ -28,6 +28,7 @@
 #include <linux/rculist.h>
 #include <linux/interrupt.h>
 #include <linux/debugfs.h>
+#include <acpi/apei.h>
 #include <asm/unaligned.h>
 
 #include "apei-internal.h"