[udev] Remove udev defines as it is the only and default one

Since hal has been replaced and removed long ago, there is no reason
to keep udev separated. Makes code easier to read and eases Makefile
maintenance.

Signed-off-by: Philippe De Swert <philippe.deswert@jollamobile.com>
[libusbg] Clean-up configuration and make libusbg module compile

configure.ac is cleaned up and now also can selectivly use libusbg
or libkmod. Also linker flags are now shown after the configure run.

Signed-off-by: Philippe De Swert <philippe.deswert@jollamobile.com>