This updates the clock handling in the DB8500 PRCMU driver with
the latest findings and API changes related to changes in the
backing firmware in the PRCMU.

- Add the necessary interfaces to get the frequencies of the
  clocks and set the rate of some of the clocks.
- Add support for controlling the clocks PLLSOC0, PLLDSI,
  DSI0, DSI1 and DSI escape clocks (DSInESCCLK).
- Correct the PLLSDI enable/disable sequence by using the
  DSIPLL_CLAMPI bit.

After this we will have the interfaces and code to implement the
U8500 clock framework properly.
Reviewed-by: NJonas Aberg <jonas.aberg@stericsson.com>
Signed-off-by: NMattias Nilsson <mattias.i.nilsson@stericsson.com>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>
Signed-off-by: NSamuel Ortiz <sameo@linux.intel.com>