drm: Introduce DRM_DEV_* log messages

This patch consolidates all the various log functions/macros into
one uber function, drm_log. It also introduces some new DRM_DEV_*
variants that print the device name to delineate multiple devices
of the same type.

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1471303084-3757-1-git-send-email-seanpaul@chromium.org