drivers/video: fsl-diu-fb: merge diu_hw into fsl_diu_data

The diu_hw structure contains two fields used to access the DIU registers,
but the only instance of this structure is a global variable, 'dr'.
Eliminate 'dr' by merging its fields into the fsl_diu_data structure,
which is instantiated on the heap for each DIU controller found.

Signed-off-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>