dm: core: Add dm_remove_devices_flags() and hook it into device_remove()

The new function dm_remove_devices_flags() is intented for driver specific
last-stage cleanup operations before the OS is started. This patch adds
this functionality and hooks it into the common device_remove()
function.

Drivers wanting to use this feature for some last-stage removal calls,
need to add one of the DM_REMOVE_xx flags to their driver .flags.

Signed-off-by: Stefan Roese <sr@denx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>