Limit udev device scan to subsystem 'input'

This change makes the call to 'udev_enumerate_scan_devices' much faster.
In particular, for some bluetooth devices, this function may implicitly
read its battery's virtual file 'uevent', e.g.

/sys/devices/*/usb1/1-1/*/bluetooth/hci0/*/power_supply/hid-*-battery/uevent

Reading this file may (for unknown reasons) block up to 10 seconds.
Since udev_enumerate_scan_devices is called 4 times (for keyboard,
mouse, touchpad, and joypad) during startup this may cause a
considerable delay.

Limiting the scan to subsystem 'input' yields the same devices but makes
the scan faster and does not read 'uevent' of the input controller's
power_supply.

input/drivers/udev_input.c

@@ -1234,6 +1234,7 @@ static bool open_devices(udev_input_t *udev,
       return false;
 
    udev_enumerate_add_match_property(enumerate, type_str, "1");
+   udev_enumerate_add_match_subsystem(enumerate, "input");
    udev_enumerate_scan_devices(enumerate);
    devs = udev_enumerate_get_list_entry(enumerate);
 

input/drivers_joypad/udev_joypad.c

@@ -574,6 +574,7 @@ static void *udev_joypad_init(void *data)
       goto error;
 
    udev_enumerate_add_match_property(enumerate, "ID_INPUT_JOYSTICK", "1");
+   udev_enumerate_add_match_subsystem(enumerate, "input");
    udev_enumerate_scan_devices(enumerate);
    devs = udev_enumerate_get_list_entry(enumerate);