[RX51] Work around acpid detection of new input devices

This is a dirty workaround for busybox's acpid not detecting new devices that are added to the system after acpid has started. On the N900, this is a problem because acpid starts earlier in the boot process than the kernel loading modules like gpio_keys (which supplies a number of input devices we want to handle with acpid). Yes, this udev rule will result in acpid restarting many times during the boot. I did say "dirty workaround"!