OMAP: DSS2: Taal: Make driver more fault tolerant

If ULPS exit fails, and the following reset fails also, Taal driver was
left in state where it thinks DSI is enabled while it really isn't,
leading to crash.

This patch checks the return value of taal_panel_reset, and if that
fails, ulps_enabled is left true, causing the driver to retry ulps exit
later.

Also the return value of taal_wake_up is checked at taal_disable, and if
wake up fails, we'll skip the power_off. This could leave the panel into
a not-quite-valid state, but there's nothing we can do about it in that
situation.

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