pinctrl: make the pinmux-pins more helpful

The debugfs file pinmux-pins used to tell which function was
enabled but now states simply which device owns the pin. Being
owned by the pinctrl driver itself means just that it's hogged
so be a bit more helpful by printing that.

ChangeLog v1->v2:
- Preserve the self-referential owner field, just clarify that
  when the pin controller states itself as owner this means
  that it's hogged.

Acked-by: Dong Aisheng <dong.aisheng@linaro.org>
Acked-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>