drivers/video: fsl-diu-fb: rename "machine_data" to "data"

"machine_data" is too long and clunky, and the "machine" part doesn't make
much sense, anyway.
Signed-off-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>