drm: align #include directives with libdrm in uapi headers

We can't use <drm/*.h> because that upsets the serach paths in libdrm.
Also, drop the circular inclusion in drm_mode.h.

v2: Actually change the right headers.

v3: Drop the #include removal per Emil's request.

Cc: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1459353292-9063-1-git-send-email-daniel.vetter@ffwll.ch