ARM: ux500: Fork MSP platform registration for step-by-step DT enablement

We've done this before and it worked well last time. Here we're
duplicating a complex registration function to ease the process
of enabling it for Device Tree. As there are quite a few steps
taken during the registration process, it makes sense to break
them up into more manageable chunks. This patch will aid us.

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>