rtc: rtc-wm8350: add support for WM8350 RTC

This adds support for the RTC provided by the Wolfson Microelectronics
WM8350.

This driver was originally written by Graeme Gregory and Liam Girdwood,
though it has been modified since then to update it to current mainline
coding standards and for API completeness.

[akpm@linux-foundation.org: s/schedule_timeout_interruptible/schedule_timeout_uninterruptible/ to prevent bogus timeout when signal_pending()]
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: David Brownell <david-b@pacbell.net>
Cc: Liam Girdwood <linux@wolfsonmicro.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>