Move set/get_mirror() from omap_dss_device to omap_dss_driver.

This is part of a larger patch-set, which moves the control from omapdss
driver to the display driver.
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@nokia.com>

The system to allow panel drivers to exists as attached to ctrl drivers
did never work very well. It is not useed, and this patch removes it to
make the driver cleaner.

For now, controller drivers need to include also the panel driver code. In
the future a proper mechanism for this should be developed, perhaps by
creating busses for controllers.
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@nokia.com>

Add more core files to DSS2.
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@nokia.com>