drm: move drv test macros out of drmP.h

Last bit the prevented us from starting to delete the drmP.h monster
includes from source files!

Also add kernel-doc while moving them.

A nice consistent drm_dev_ prefix would be cute for these, but since
they're used everywhere I've figured I'll leave this bikeshed aside
for now.

Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180709084016.23750-2-daniel.vetter@ffwll.ch