this function is used by several board together with board_video_skip
to detect if hdmi is plugged is order to select the display to use.
So move it in imx-common to share it.

Signed-off-by: Eric Bénard <eric@eukrea.com>

this function is shared by several boards and thus can be factorized

Signed-off-by: Eric Bénard <eric@eukrea.com>
Acked-by: Eric Nelson <eric.nelson@boundarydevices.com>
Acked-by: Stefano Babic <sbabic@denx.de>