drm/print: add drm_dbg_printer() for drm device specific printer

drm/print: add drm_dbg_printer() for drm device specific printer

We've lacked a device specific debug printer. Add one. Take category
into account too.

__builtin_return_address(0) is inaccurate here, so don't use it. If
necessary, we can later pass __func__ to drm_dbg_printer() by wrapping
it inside a macro.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Luca Coelho <luciano.coelho@intel.com>
Acked-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/48607d58e5cdf8341ffdd522257542fa2ce41a19.1705410327.git.jani.nikula@intel.com