mfd: Move to the new db500 PRCMU API

Now that we have a shared API between the DB8500 and DB5500
PRCMU's, switch to using this neutral API instead. We delete the
parts of db8500-prcmu.h that is now PRCMU-neutral, and calls will
be diverted to respective driver. Common registers are in
dbx500-prcmu-regs.h and common accessors and defines in
<linux/mfd/dbx500-prcmu.h> This way we get a a lot more
abstraction and code reuse.

Signed-off-by: Mattias Nilsson <mattias.i.nilsson@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>