ivi-shell: Move functions that are not used by other to private.h from export.h.

> +WL_EXPORT int32_t +ivi_layout_surface_get_dimension(struct
> ivi_layout_surface ivisurf, + int32_t dest_width, int32_t +*dest_height)
> Does this function need to be WL_EXPORT?
> hmi-controller does not use it, and it is exposed to ivi-shell.so via
> struct ivi_layout_interface.

For the time being, there are some APIs which is not used by
hmi-controller.c. but it is used by ivi-controller.so maintained by
another project. I will add reference implementation for them later in
hmi-controller.c

Signed-off-by: Nobuhiko Tanibata <NOBUHIKO_TANIBATA@xddp.denso.co.jp>