[Qemu-arm] arbitrarily address wirte in pxa2xx_pm_write

[sohu0106]

in function pxa2xx_pm_write()[hw/arm/pxa2xx.c] with qemu version under 4.0-rc4 
do not check the addr rang in the default case, it will lead 
to arbitrarily address write in guest.


 137     default:    /* Read-write registers */
 138         if (!(addr & 3)) {
 139             s->pm_regs[addr >> 2] = value;
 140             break;
 141         }