plat/arm files should only be used by Arm platforms. If other platforms
use them, they create dependencies that can introduce problems when
updating Arm platforms.

This patch copies the needed code from Arm platforms so that poplar can
be independent from them.

Change-Id: I0b194f5bdb0377b8ccacbd400e021614c026c7fe
Tested-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>