drm/client: Fix drm client endless Kconfig loop

drm/client: Fix drm client endless Kconfig loop

if DRM_CLIENT_SELECTION is enabled, and none of the client is, the
"Default DRM Client" choice is empty, and this makes Kconfig goes
into an infinite loop of:

  Default DRM Client
  choice[1-0?]: 0
  Default DRM Client
  choice[1-0?]: 0
  Default DRM Client
  choice[1-0?]: 0
  ....

So only allow the choice if at least one of the client is selected.

Fixes: f7b42442c4ac ("drm/log: Introduce a new boot logger to draw the kmsg on the screen")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/dri-devel/20241204160014.1171469-1-jfalempe@redhat.com/T/#md78853bba8904fd7614073f280f721d13ab0b432
Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>
Tested-by: Dan Carpenter <dan.carpenter@linaro.org>
Acked-by: Simona Vetter <simona.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20241212091153.1592096-1-jfalempe@redhat.com