The Nomadik Pinctrl driver requires access to some PRCMU registers
in order to run with full functionality. When Device Tree is
disabled the required PRCMU base address is passed in via platform
data, so in order for Device Tree booting to be as functional, we
need a similar mechanism to fetch it from Device Tree.

The new semantics goes like this: Parse the Device Tree and look
for the PRCMU node using a provided Phandle. Obtain the ioremaped
address from that node. If one was supplied via platform data
over-write it with anything found in Device Tree. Fail if either
the prcm_base can't be found if we're running on anything other
than an STN8815 ASIC.
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>