drm: xlnx: zynqmp_dpsub: Rename zynqmp_dpsub_handle_vblank with DRM prefix

The better convey its purpose, rename the zynqmp_dpsub_handle_vblank()
function that belongs to the DRM layer to
zynqmp_dpsub_drm_handle_vblank().

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

drm: xlnx: zynqmp_dpsub: Decouple DRM device from zynqmp_dpsub

To complete the decoupling of the DRM device from the zynqmp_dpsub,
group all DRM-related structures in a zynqmp_dpsub_drm structure and
allocate it separately from the zynqmp_dpsub. The DRM managed allocation
of the drm_device now doesn't cover the zynqmp_dpsub anymore, so we need
to register a cleanup action to release the zynqmp_dpsub when the
drm_device is released.

The will allow usage of the DisplayPort encoder as a standalone bridge,
without registering a DRM device in this driver.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

drm: xlnx: zynqmp_dpsub: Move all DRM init and cleanup to zynqmp_kms.c

Continue the isolation of DRM/KMS code by moving all DRM init and
cleanup from zynqmp_dpsub.c to zynqmp_kms.c.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

drm: xlnx: zynqmp_dpsub: Move CRTC handling to zynqmp_kms.c

Decouple the CRTC handling from the display controller programming by
moving the corresponding code from zynqmp_disp.c to zynqmp_kms.c. This
prepares for using the DPSUB with a live video input, without creating a
DRM CRTC in the DPSUB driver.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

drm: xlnx: zynqmp_dpsub: Move DRM/KMS initialization to separate file

Start preparation for using the DPSUB as a standalone DisplayPort
encoder without a display controller by moving the DRM/KMS
initialization to a new zynqmp_kms.c file. No functional change
intended.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>