vulkan/wsi/wayland: fold wsi_wl_display_swrast and wsi_wl_display_dmabuf into parent

vulkan/wsi/wayland: fold wsi_wl_display_swrast and wsi_wl_display_dmabuf into parent

The two structs wsi_wl_display_swrast and wsi_wl_display_dmabuf have in
common the list of formats and the only difference between both is the
interface object.

As we know that only one of the arrays is populated (we never bind to
wl_shm and the dmabuf interface simultaneously), we can move the members
of these structs to wsi_wl_display and simplify the code.

This is based on previous work of Simon Ser <contact@emersion.fr>.

Signed-off-by: Simon Ser <contact@emersion.fr>
Signed-off-by: Leandro Ribeiro <leandro.ribeiro@collabora.com>
Reviewed-by: Eric Engestrom <eric@engestrom.ch>
Acked-by: Daniel Stone <daniels@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12117>