drm/cirrus: Move primary-plane format arrays

Move the primary plane's format and modifier arrays within the
source file and adapt naming slightly. No functional changes.

Done in preparation of converting cirrus to regular atomic helpers.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230215161517.5113-8-tzimmermann@suse.de