drm: drop i386 verification

Linux doesn't run on i386, anymore. See:

    commit d55c5a93db2d5fa95f233ab153f594365d95b777
    Author: H. Peter Anvin <hpa@linux.intel.com>
    Date:   Wed Nov 28 11:50:24 2012 -0800

        x86, 386 removal: Remove CONFIG_CMPXCHG

        All 486+ CPUs support CMPXCHG, so remove the fallback 386 support
        code.

Furthermore, as the commit-message states, all 486+ CPUs support the
CMPXCHG instruction and thus even legacy DRM can run fine.

Drop the now superfluous "x86 == 3" check.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>