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