arm64: perf_event: Add missing header needed for smp_processor_id()

In perf_event.c we use smp_processor_id(), but we haven't included
<linux/smp.h> where it is defined, and rely on this being pulled in
via a transitive include. Let's make this more robust by including
<linux.smp.h> explicitly.
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Raphael Gault <raphael.gault@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>

arch/arm64/kernel/perf_event.c

@@ -19,6 +19,7 @@
 #include <linux/of.h>
 #include <linux/perf/arm_pmu.h>
 #include <linux/platform_device.h>
+#include <linux/smp.h>
 
 /* ARMv8 Cortex-A53 specific event types. */
 #define ARMV8_A53_PERFCTR_PREF_LINEFILL				0xC2