mfd: prcmu: pass a base and size with the early initcall

This patch will make an early remapping of the PRCMU, to be
used when setting up the clocks, that will call down into parts
of the PRCMU driver before it is probed.

Going forward this will be removed like this:

- The mailbox subsystem need to be merged.
  http://marc.info/?l=linux-kernel&m=136314559201983&w=2



- At this point the PRCMU clock code can be moved over to the
  ux500 clock driver in drivers/clk/ux500/* and maintained
  there in a decentralized manner.

- This early initcall and PRCMU base parameters become part of
  the ux500_clk_init() call instead.

Cc: Suman Anna <s-anna@ti.com>
Cc: Loic Pallardy <loic.pallardy@st.com>
Acked-by: Samuel Ortiz <sameo@linux.intel.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>