drm/bochs: Use regular atomic helpers

Remove the simple display pipeline in favor of the regular atomic
helpers in bochs. The simple-pipe helpers are considered deprecated
in DRM.

This effectivly inlines the simple-pipe code for plane and CRTC
support. Instead of a single update helper, there's now a mode-set
helper for the CRTC and an update helper for the plane. The encoder
changes type from NONE ot VIRTUAL.

Removing simple-pipe helpers from bochs will allow for related
cleanups in GEM VRAM helpers.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240902105546.792625-8-tzimmermann@suse.de