target/ppc/pmu: Include missing 'qemu/timer.h' header

Since commit c2eff58 ("target/ppc: PMU basic cycle count for
pseries TCG") pmu_update_cycles() uses QEMU_CLOCK_VIRTUAL and
calls qemu_clock_get_ns(), both defined in "qemu/timer.h".

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20230828221314.18435-2-philmd@linaro.org>

target/ppc/power8-pmu.c

@@ -16,6 +16,7 @@
 #include "exec/exec-all.h"
 #include "exec/helper-proto.h"
 #include "qemu/error-report.h"
+#include "qemu/timer.h"
 #include "qemu/main-loop.h"
 #include "hw/ppc/ppc.h"
 #include "power8-pmu.h"