hw/intc/xics: Include missing 'cpu.h' header

Include missing headers in order to avoid when refactoring
unrelated headers:

  hw/intc/xics.c: In function 'icp_realize':
  hw/intc/xics.c:304:5: error: unknown type name 'PowerPCCPU'
    304 |     PowerPCCPU *cpu;
        |     ^~~~~~~~~~

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

hw/intc/xics.c

@@ -40,6 +40,7 @@
 #include "hw/irq.h"
 #include "sysemu/kvm.h"
 #include "sysemu/reset.h"
+#include "target/ppc/cpu.h"
 
 void icp_pic_print_info(ICPState *icp, Monitor *mon)
 {