pinctrl: pinctrl-single: pin names for pinctrl-single.bits

Take care to name pin names as
register-offset.bit-pos-of-pin-in-register in case configuring multiple
pins in register.

Signed-off-by: Manjunathappa, Prakash <prakash.pm@ti.com>
Acked-by: Haojian Zhuang <haojian.zhuang@gmail.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>