loader: move loader_open_device out of HAVE_LIBUDEV block

loader: move loader_open_device out of HAVE_LIBUDEV block

Fixes the following build issue, when building without libudev.

CCLD   libGL.la
./.libs/libglx.a(dri2_glx.o): In function `dri2CreateScreen':
src/glx/dri2_glx.c:1186: undefined reference to `loader_open_device'
collect2: ld returned 1 exit status

CCLD     libEGL.la
Undefined symbols for architecture x86_64:
"_loader_open_device", referenced from:
  _dri2_initialize_x11_dri2 in libegl_dri2.a(platform_x11.o)

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91077
Signed-off-by: Julien Isorce <j.isorce@samsung.com>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>