OMAPDSS: remove omap_dss_device's suspend/resume

The panel drivers contain enable, disable, suspend and resume calls.
The suspend and resume are effectively identical to disable and enable.

This patch removes panel suspend and enable code from omapdss and the
panel drivers, and replaces their use with enable and disable.

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