ARM: ux500: Move all Device Tree booting into cpu-db8500

To aid the kernel in its effort to move to DT only booting, we're
transplanting all Device Tree related code to cpu-db8500 which will
remain persistent throughout the transition. This change paths the
way for complete removal of board-mop500, which will be done once
the all DMA settings are moved into the respective DT source files.

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