drm: xilinx: crtc: Switch to drm_crtc_init_with_planes()

As the universal plane has been added, the legacy drm_crtc_init()
was changed to allocates a primary plane implicitly. It results in
2 planes allocated for one Xilinx DRM CRTC. Replacing drm_crtc_init()
call with drm_crtc_init_with_planes() fixes this, and the CRTC's
private plane is passed as an argument to this call.

Signed-off-by: Christian Kohn <christian.kohn@xilinx.com>
Signed-off-by: Hyun Kwon <hyun.kwon@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>