staging: drm/imx: Add support for VGA via TVE on i.MX53

This adds display interface timings for the Television Encoder
connected to IPU DI1 on i.MX53 and adds some configuration
glue code to select which IPU signal generators / pins are to
be used for HSYNC/VSYNC signals.

The default configuration is pin2/pin3 for hsync/vsync. The
VGA connector on i.MX53-QSB uses pin7/pin8, and the analog
part of the DVI-I connector on MBa53 connects to pin4/pin6.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>