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.
d0612f906d