target/xtensa/cpu: Include missing "memory.h" header

Under system emulation, xtensa_cpu_initfn() calls
memory_region_init_io(), itself declared in "exec/memory.h".

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20221217172907.8364-10-philmd@linaro.org>

target/xtensa/cpu.c

@@ -35,6 +35,9 @@
 #include "qemu/module.h"
 #include "migration/vmstate.h"
 #include "hw/qdev-clock.h"
+#ifndef CONFIG_USER_ONLY
+#include "exec/memory.h"
+#endif
 
 
 static void xtensa_cpu_set_pc(CPUState *cs, vaddr value)