drivers/rtc/rtc-as3722: add RTC driver

The ams AS3722 is a compact system PMU suitable for mobile phones, tablets
etc.

Add a driver to support accessing the RTC found on the ams AS3722 PMIC
using RTC framework.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: Florian Lobmaier <florian.lobmaier@ams.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>