bus: ti-sysc: Implement display subsystem reset quirk

The display subsystem (DSS) needs the child outputs disabled for reset.
In order to prepare to probe DSS without legacy platform data, let's
implement sysc_pre_reset_quirk_dss() similar to what we have for the
platform data with omap_dss_reset().

Note that we cannot directly use the old omap_dss_reset() without
platform data callbacks and updating omap_dss_reset() to understand
struct device. And we will be dropping omap_dss_reset() anyways when
all the SoCs are probing with device tree, so let's not mess with the
legacy code at all.

Cc: Jyri Sarha <jsarha@ti.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>