drm: omapdrm: Remove nested PM get/sync when configuring encoders

The omap_crtc_encoder_setup() function is always called with the DSS
enabled. Remove the dispc_runtime_get() and dispc_runtime_put() calls.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>