mfd: dbx500-prcmu: Move PRCMU numerical clock identifiers into DT include file

These are required to request DBx500 PRCMU clocks from Device Tree. The
numbers used are taken directly from the Hardware Specification document.
We're moving them from the DBx500 PRCMU include file into the DT include
directory and referencing them from the former via a #include.

Acked-by: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>