ARM: Kirkwood: Fix the internal register ranges translation

Although the internal register window size is 1 MiB, the previous
ranges translation for the internal register space had a size of
0x4000000. This was done to allow the crypto and nand node to access
the corresponding 'sram' and 'nand' decoding windows.

In order to describe the hardware more accurately, we declare the
real 1 MiB internal register space in the ranges, and add a translation
entry for the nand node to access the 'nand' window.

This commit will make future improvements on the MBus DT binding easier.

Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>