Avoid using hard-coded SoC's register address in mptramp code for Armada XP

SoC's registers base address may differ between boards
(0xf1000000 or 0xd0000000). Therefore, in order to use
the proper CPU Boot Address Redirect register during SMP
initialization in mptramp the real, physical address has
to be passed to mptramp based on the value from DT.

Reviewed by: gber