Documentation: devres: add missing PINCTRL helpers

Add devm_pinctrl_get_select() and devm_pinctrl_register_and_init() to
devres.rst.

Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Link: https://lore.kernel.org/r/20220922153737.2863951-1-yangyingliang@huawei.com


Signed-off-by: Jonathan Corbet <corbet@lwn.net>