udev: bump to 181 and other fixes

Changes:
- Linux kernel requirement: 2.6.34 and above (devtmpfs is mandatory)
(this also applies to the chosen toolchain, because of Kernel headers)
- optional dependency on libusb and usbutils removed
- added dependency on kmod
- added dependency on util-linux for libblkid
- install in /lib/udev instead of /usr/libexec/udev
- udevd moved to /lib/udev
- fixed path to pci.ids and usb.ids
- persistent rules generator is disabled by default, so option
is introduced to enable this option if desired

[Peter: fix build on uClibc, Config.in tweaks]
Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>