pinctrl: samsung: Add support for SoC-specific suspend/resume callbacks

SoC-specific driver might require additional save and restore of
registers. This patch adds pair of SoC-specific callbacks per pinctrl
device to account for this.

Signed-off-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Tested-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>