Install libgudev-1.0.so in prefix / instead of prefix /usr

Install libgudev-1.0.so in prefix / instead of prefix /usr

This is to match where libudev.so is installed and it works because
all dependent libraries are already installed in / instead of /usr on
most distros:

 $ ldd /usr/lib64/libgudev-1.0.so
         linux-vdso.so.1 =>  (0x00007fff44dff000)
         libudev.so.0 => /lib64/libudev.so.0 (0x0000003bf2600000)
         libgobject-2.0.so.0 => /lib64/libgobject-2.0.so.0 (0x0000003fb5200000)
         libgthread-2.0.so.0 => /lib64/libgthread-2.0.so.0 (0x0000003fb4e00000)
         libpthread.so.0 => /lib64/libpthread.so.0 (0x0000003d5b000000)
         librt.so.1 => /lib64/librt.so.1 (0x0000003d5b800000)
         libglib-2.0.so.0 => /lib64/libglib-2.0.so.0 (0x0000003fb4a00000)
         libc.so.6 => /lib64/libc.so.6 (0x0000003d5ac00000)
         /lib64/ld-linux-x86-64.so.2 (0x0000003d5a800000)

With this change it is possible to write libgudev applications that
can be installed in /bin or /sbin and can run without /usr being
mounted. This is needed for e.g. udisks, NetworkManager and other
subsystem-specific daemons.

Signed-off-by: David Zeuthen <davidz@redhat.com>