pinctrl: starfive: jh7110: Add system pm ops to save and restore context

Add system pm ops to save and restore pinctrl registers
when suspending and resuming the driver, respectively.

Signed-off-by: Hal Feng <hal.feng@starfivetech.com>
Link: https://lore.kernel.org/r/20230905122105.117000-3-hal.feng@starfivetech.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>