dm: core: Add a flag for power domain control on device removal

In various cases a power domain must stay enabled after device
removal when booting OS (i.e. serial debug console or display).
Add a flag to selectively skip switching off a power domain.

Fixes: 52edfed6 ("dm: core: device: switch off power domain after device removal")
Signed-off-by: Anatolij Gustschin <agust@denx.de>
Acked-by: Neil Armstrong <narmstrong@baylibre.com>
Tested-by: Guillaume La Roque <glaroque@baylibre.com>
Reviewed-by: Simon Glass <sjg@chromium.org>