arm: mvebu: Enable NAND controller on MVEBU SoC's

arm: mvebu: Enable NAND controller on MVEBU SoC's

This patch enables the NAND controller on the Armada XP/38x and provides
a new function that returns the NAND controller input clock. This
function will be used by the MVEBU NAND driver.

As part of this patch, the multiple BIT macro definitions are moved
to a common place in soc.h.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Peter Morrow <peter@senient.com>
Cc: Luka Perkov <luka.perkov@sartura.hr>