drm/client: Fix: drm_client_new: Don't require DRM to be registered

drm/client: Fix: drm_client_new: Don't require DRM to be registered

Commit 894a677f4b3e ("drm/cma-helper: Use the generic fbdev emulation")
broke almost all drivers that use the CMA helper.

The reason is that drm_client_new() requires that the DRM device has
been registered, but the drivers register fbdev before registering DRM.

Remove the requirement that DRM should be registered when creating a
new client.

Fixes: c76f0f7cb546 ("drm: Begin an API for in-kernel clients")
Cc: Maxime Ripard <[email protected]>
Cc: Icenowy Zheng <[email protected]>
Cc: Chen-Yu Tsai <[email protected]>
Cc: Daniel Vetter <[email protected]>
Signed-off-by: Noralf Trønnes <[email protected]>
Tested-by: Icenowy Zheng <[email protected]>
Reviewed-by: Daniel Vetter <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]