drm: zynq_drm: osd: Fix to allocate layers in probe()

Fix to allocate osd layers in probe(), and return one layer
when requested by client(zynq_drm_plane). Fix returning
error codes accordingly.

Signed-off-by: hyun woo kwon <hyunk@xilinx.com>
drm: zynq_drm: osd: Change reg-update functions as external

Reggister-update functions were used internally in osd.c,
but this patch changes those as external functions. Clients(plane.c)
can place those functions more properly.

Signed-off-by: hyun woo kwon <hyunk@xilinx.com>
drm: zynq_drm: drv: Modify debug message functions

Modify debug message functions. Create a function in c, and
move some definitinos from a header to drv.c.

Signed-off-by: hyun woo kwon <hyunk@xilinx.com>
drm: zynq_drm: plane: Prepare a dma desc in commit()

Fix to prepare a dma descr in commit(). It was done in mode_set(),
and it could happen that some operation fails and a descriptor remains
in the pending queue. It cannot happen with The zynq_drm implemention
at that time, but it's safer to remove a potential bug.

Signed-off-by: hyun woo kwon <hyunk@xilinx.com>