Qt-embedded can be used on multiple screens by using environment variables
QWS_DISPLAY, QWS_MOUSE_PROTO, et cetera.

The gstreamer element mfw_v4lsink used to accelerate media playback on i.MX
devices can also be pointed at different displays through the 'device'
property, but the current acceleration patch doesn't have a mechanism for
setting the property, and always uses the compiled-in default.

This patch allows userspace startup code to override the default through
the use of the 'v4lsinkdev' environment variable.

Please refer to the Qt4-embedded documentation for proper usage of the
QWS_x environment variables and the Freescale Multimedia documentation
for descriptions of the various gstreamer elements.

A sequence of this for a secondary display might be this:

	export QWS_DISPLAY=linuxfb:/dev/fb2:1
	export v4lsinkdev=/dev/video19
	my-qt-app -qws

Signed-off-by: Eric Nelson <eric.nelson@boundarydevices.com>