pinctrl: sprd: Add CM4 sleep mode support

pinctrl: sprd: Add CM4 sleep mode support

For the new Spreadtrum pin controller, it expands 6bits to describe the
pin sleep mode with adding one CM4_SLEEP mode, which means the pin sleep
related configuration will be loaded automatically by hardware when the
CM4 system goes into deep sleep mode.

Signed-off-by: Bruce Chen <bruce.chen@unisoc.com>
Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Link: https://lore.kernel.org/r/8ae52263b0625c416461821c457e6789b67170b6.1571228451.git.baolin.wang@linaro.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>