tps65950: driver for the TPS65950 PMIC

Change-Id: I6b6163e59233d1f823f03550b949d53e1738a7f4
readclock: add support for the TPS65950 RTC

On the BeagleBoard-xM, the RTC is located on the Power Management IC
(PMIC). To keep things consistent, access to the PMIC's RTC is done
through the readclock driver. The readclock driver forwards the request
on to the TPS65950 driver which does the work of manipulating the
registers on the chip.

Change-Id: I53cefbb59c5a9ab87fab90df3cc1a75a6e430f58