drm: Use userspace compatible type in fourcc_mod_code macro

drm: Use userspace compatible type in fourcc_mod_code macro

__u64 should be used instead of u64.

Feature originally added in:

commit 33cc1b3b1530d4ccb8b9abc3a94b42bbe7405b13
Author: Rob Clark <robdclark@gmail.com>
Date:   Thu Feb 5 14:41:52 2015 +0000

    drm: add support for tiled/compressed/etc modifier in addfb2

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Rob Clark <robdclark@gmail.com>
Cc: Daniel Stone <daniels@collabora.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: dri-devel@lists.freedesktop.org
Cc: stable@vger.kernel.org # v4.1+
Fixes: 33cc1b3b1530 ("drm: add support for tiled/compressed/etc modifier in addfb2")
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1442999431-28568-1-git-send-email-tvrtko.ursulin@linux.intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>