configure: libdrm is a single package

configure: libdrm is a single package

The intent of the libdrm_$driver version limits has always been to not
burden the "other" drivers with updating their libdrm unless really
necessary. Unfortunately the configure script erroneously only checked
the driver-specific bit and not the generic bit of libdrm as well. Fix
this.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Chad Versace <chadversary@chromium.org>
Reviewed-by: Dave Airlie <airlied@redhat.com>