OMAP: DSS2: DSI: add parameter to enter ulps on disable

Add parameter to omapdss_dsi_display_disable() which the panel driver
can use to tell if the DSI lanes should be put to ULPS before disabling
the interface.

This can be used to skip ULPS entry in cases where the panel doesn't
care about ULPS state, for example when the panel will be reset, or when
the display interface will be enabled again right after the disable.

This will speed up the operation considerably in cases where entering
ULPS would fail with timeout, and the panel driver isn't even interested
in entering ULPS.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>