mfd: da9062: Support for the DA9063 RTC in the DA9062 core

Add MFD core driver support for a RTC component

- MFD core adds the RTC resources da9062_rtc_resources[] for the RTC
  alarm and tick timer IRQ
- An appropriate mfd_cell has been added into da9062_devs[] to support
  a component .name = "da9062-rtc" and .of_compatible  = "dlg,da9062-rtc"

Signed-off-by: Steve Twiss <stwiss.opensource@diasemi.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>