loader: ifdef libdrm specific code and include

loader: ifdef libdrm specific code and include

Mesa provides the flexibility of building without the
need to have libdrm present on the system. The situation
has regressed with the recent commit

commit 8c2e7fd8460750543367053b1be9368cc38e1d6a
Author: Emil Velikov <emil.l.velikov@gmail.com>
Date:   Fri Jan 10 23:36:16 2014 +0000

    loader: introduce the loader util lib

By isolating libdrm code by #ifndef __NOT_HAVE_DRM_H we
can have libdrm-less builds on across all build systems.

This patch converts Android's _EGL_NO_DRM to __NOT_HAVE_DRM_H
to provide consistency with the other cases within mesa, allows
compilation of libloader on libdrm-less scons and conditionally
links against libdrm if present under automake.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=73776
BUgzilla: https://bugs.freedesktop.org/show_bug.cgi?id=73777
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>