pinctrl: Enable device link creation for pin control

A pin controller may want to create a link between itself
and its clients to be sure of suspend/resume call ordering.

Introduce link_consumers field in pinctrl_desc structure to let
pinctrl core knows that controller expect to create a link.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@st.com>
[Renamed create_link to link_consumers]
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>