u8500: Moving processor-specific functions to cpu area.

Functions such as providing power to the MMC device and reading
the processor version register should be in the cpu area for
access by multiple u8500-based boards.

Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: John Rigby <john.rigby@linaro.org>
Signed-off-by: Tom Rini <trini@ti.com>