drm/fb-helper: Always initialize generic fbdev emulation

Initialize the generic fbdev emulation even if it has been disabled
on the kernel command line. The hotplug and mode initialization will
fail accordingly.

The kernel parameter can still be changed at runtime and the emulation
will initialize after hotplugging the connector.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221103151446.2638-20-tzimmermann@suse.de