pinctrl: single: Add request() api

Add pinctrl_ops->request api to configure pctrl
pad register in gpio mode.

Signed-off-by: Rayagonda Kokatanur <rayagonda.kokatanur@broadcom.com>
Signed-off-by: Bharat Gooty <bharat.gooty@broadcom.com>
Acked-by: Rayagonda Kokatanur <rayagonda.kokatanur@broadcom.com>
Reviewed-by: Simon Glass <sjg@chromium.org>