drm-formats: remove create() and destroy() from the API

Since commit "drm-formats: save result of intersection in the first
array", every block of code where weston_drm_format_array_create() and
destroy() are being called could use init() and fini() instead.

Remove these two functions from the API to make it leaner. This patch
also modifies the code that depends on these functions to use init() and
fini().

Signed-off-by: Leandro Ribeiro <leandro.ribeiro@collabora.com>
Reviewed-by: Alexandros Frantzis <alexandros.frantzis@collabora.com>