staging: drm/imx: Add support for Television Encoder (TVEv2)

This driver adds support for the Television Encoder integrated
on i.MX53 SoCs (TVEv2).

Currently only the VGA output mode is supported, which only uses
the TVDAC to generate RGB levels. HSYNC and VSYNC signals are
routed directly from the IPU signal generator pins through IOMUXC.

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